Dragon applications
A long, long time ago, there was a space program to put a man on the Moon. It was a magnificent achievement. Maybe for the wrong reasons, but still, that was probably the most notable event of 20th century.
Even before the great success was achieved, huge cost of the undertaking made many government heads a little bit sober. This could not be sustained. But the whole development and production ecosystem was built around that. And so, as Apollo winded down, Apollo Applications Program was born. There were many great ideas foreseen in the program, of which only Skylab and Apollo/Soyuz rendezvous were realized. But in many ways, this program could be seen as a precursor of ISS.
Ever since Apollo, NASA appeared as living of the old glory. Using a "shoestring" budget compared to Apollo, it seems unable to repeat the glorious achievements of the past. Despite Voyagers, first reusable spacecraft, space telescopes, long duration Mars rovers, in-space construction and assembly, permanent 20-year manned presence in space, somehow that was not enough to match high expectations set by Apollo 11.
Every few years there is new initiative, a new vision made by presidents. Go back to the Moon. No, go to the Mars. No, lets do asteroids first. Maybe Moon again? Why not just a deep space station? But for decades, such human exploration initiatives just fall short. It just does not work. Presidents come and go. Some stay four years, some eight. The next president wants near term results. Something sexy and dramatic. In four years. And that it does not cost much. Because president does not approve the budget. And frankly, achievement seeking space program is not really worth various trade-offs that politicians need to make to get the funding.
So what gets funded? International cooperation and commitments. Once there is foreign policy commitment to some program (such as ISS or LOP-G), there is high cost of backing down. For a nation that sees itself as a global leader. Also, local politicians like to support local, aerospace industry. Especially if they don't have so much of high tech to offer (yes, I am talking about Alabama). Incremental, low risk improvements are preferred. Risk should be reduced as much as possible. Because any failure, especially loss of human life, causes multi-year delay or even program cancellation.
Will Artemis survive long-term? Will SLS be successful? Or LOP-G? Or ISS? Or Axiom commercial space station? I cannot predict the future. But for many space enthusiasts, SpaceX and Elon Musk has been a savior of space-faring future. Other programs have consistently been over budget and so expensive they could not be sustained long term. Although launch and equipment costs have decreased over the decades, due to "feature creep", push to develop and test new things in space, ever decreasing risk tolerance, there is appearance of snail-paced progress.
SpaceX has changed that paradigm. It developed low-cost rocket. It iterated it to increase trust and capacity from Falcon 9 V1.0 to latest Falcon Heavy almost ten times. It developed low cost first stage and fairing re-usability. SpaceX managed to decrease launch cost per kilogram (compared to EELV program) almost five times.
While all eyes are focused on next generation Starship development, which promises another order of magnitude cost reduction, Dragon 2 based architecture is just entering operational phase. Last year we had Demo-1 launch to ISS. Demo-2 first crewed flight is planned for May. Followed by first long term crew flight USCV-1 in August. And first Dragon 2 resupply mission in September. Three Dragon 2 missions planned just for this year. So Dragon 2 will have steady pipeline of four to six missions every year. Without other space tourist missions that might commence from next year.
Latest, a little bit lukewarm announcement was selection of Dragon XL as Lunar Gateway resupply provider. A new variant that has really scarce details. All that is known is payload mass of 5000 kg and one rendering. So why is Dragon XL a game changer for NASA and lunar exploration?
We know that Elon Musk is a big fan of re-usability. Sure, they could develop Dragon XL as a throwaway capsule much like Cygnus. Just remove unneeded head shield, change the outer mold to have more internal space and repackage existing technology. Easy money, that can be used to fund Starship and Starlink development. SpaceX should not spend a dime to go beyond and above NASA requirements. After all, Boeing will not do it. Northrop Grumman will not do it. And that is why they can slowly respond.
But the fact is, Elon Musk cannot be sure when and if Starship will be operational. Nor how much money will go down the drain. Mk1, SN1, SN2, SN3 and interim test tanks have all failed. They switch body material from Al-Li to composites to stainless steel. And God knows how many failures are awaiting with reentry and landing efforts. Not to mention life support and MMOD resiliency.
For Starlink, booster and fairing reuse have been the backup plan that enables much cheaper launch capacity, that might allow SpaceX to avoid bankruptcy. So it is clear that SpaceX is trying to pursue all funded missions possible. And that is why Dragon XL is important.
Artemis and Lunar Gateway are highly dependent upon SLS, a poster child of inefficient and bloated government program. Like a zombie, shuttle derived technology survived for half a century with just a minor changes. And it has been impossible to kill, since there was no alternative. Yes, there was distributed launch idea based on EELV/ULA. But it is not proven nor available now. And with ULAs parents, any such alternative would end up similar to SLS.
So how could one supply vehicle change this? And make SLS obsolete? Well, if Dragon XL will just be like Cygnus with IDSS port, it will not change much. SpaceX could earn good money for it, making it single purpose vehicle designed for one purpose and one purpose only. Paired with Falcon Heavy and existing propulsion and fuel capacity, it can reach the gateway. But can SpaceX do more with minor changes?
First, all vehicles coming to Lunar Gateway (with the exception of Lunar Ascent Vehicle) will not be reusable. Ok, Orion should be. Except the service module. And the heat shield. So with moderate additional deltaV, Dragon XL could perform aerobraking to LEO using Earth atmosphere. Since it is coming from cis-lunar space, there is no need for heat-shield. Even bring just 20m/s on single pass through upper atmosphere should be sufficient to aerobrake to LEO in less than six months. Yes, it will pass through Van-Allen belts many times. But it should be designed to sustain this crossing anyway.
Once in LEO, what can be done with it? Well, if SpaceX could design its docking port to be both active and passive at the same time...maybe they could launch crew dragon to LEO. Two astronauts with logs of bags, dock with Dragon XL and transfer the cargo from Crew Dragon to XL. Expendable parts? Ok, probably there is no way to cram 5000kg of bags together with two astronauts into the Crew Dragon. Maybe that is bad idea. And it might be a little bit hard to design IDSS port for both active and passive mode. But the same Dragon XL could dock to ISS. And then transfer the equipment from other supply vehicles to Dragon XL. After all, what are these space tourists going to do for days on ISS? Talking with REAL astronauts? Gazing from cupola whole day? Well...they could carry bags around. It might be easier than on Earth!
One nice thing about this approach is that if would provide cargo return capability from Lunar Gateway to the Earth. In the future, samples collected by probes and rovers from comets, Mars or Moon could be brought to Lunar Gateway first. Even analysed there. You know, planetary protection and stuff. But that is far in the future.
Once that Dragon XL is docked to ISS and fully loaded, it can undock. But there is a problem. It can have new cargo for lunar gateway. But there is no propellant to get there. It requires nearly 4km/s delta-V to get to the Lunar Gateway. Plus fuel to return back. So what Dragon XL really needs is a tank full of propellant. And a lots of it. Such a tank could be launched on separate Falcon Heavy flight.
In fully reusable configuration Falcon Heavy could launch around 28 tons to LEO. So that would be ideal mass of the tank full of MMH/NTO propellant. What should such a tank have? Well, it needs passive IDSS port so that Dragon XL can dock to it. It needs some solar panels. Maybe the same as Dragon XL, or attached around the trunk like Dragon 2. But it could reuse many systems from Dragon 2 or Dragon XL. Heck, it can even BE a special variant of Dragon 2, filled with additional MMH/NTO fuel. Its 9m3 of pressurized and 12m3 of unpressurized cargo space could be used for additional tanks. It could be designed to automatically dock with Dragon XL and transfer fuel. Assuming 21m3 of volume and propellant density of 1200kg/m3, Such Tank Dragon variant could provide at least 20 tonnes of propellant to Dragon XL. Plus, it could also dock with ISS and perform ISS reboost as needed. This could be done by single Draco thruster, similar to ISS reboost experiment done with Cygnus.
An obvious requirement for Dragon XL would be to have similarly sized tanks, that could hold 20 tons of fuel. And note that this could be a limiting factor for payload mass to gateway, highly dependent upon dry mass of Dragon XL.
How would fuel transfer be performed? IDSS standard does not specify this, but it has been foreseen as future enhancement. But the transfer is not so easy - it requires three connectors - for fuel (MMH), oxidizer (NTO) and pressure gas (He). In the spirit of androgynous docking design and two-way fuel transfer capability, it will probably be symmetric and distributed in the keep-clear zones of IDSS dock. This would be the major new capability that would require NASA clearance (and ideally funding support). But that would allow full resupply chain from Earth to ISS to Lunar gateway and back. It would require two launches (Falcon Heavy/Tank Dragon and Falcon 9/Cargo Dragon) instead of one. And additional astronaut time to transfer cargo through ISS. But the only discard-able parts of the infrastructure would be two Falcon upper stages and a single Dragon trunk.
With this capability, Cargo Dragon could also act as a space tug from GTO to GEO and back to LEO for geostationary satellites. Now all that is nice, but how could this make Dragon XL an SLS killer? After all, only SLS can launch Orion to the Gateway, right? Well...reusable Falcon Heavy can launch Orion to the ISS. Since it is not man-rated, it can launch it without crew and escape tower. Not bad. And crew can hang out and chill on the ISS, coming with the flight proven ....Starliner. Since they have nothing to do, they might transfer the cargo around. But that is not really important right now. So, Orion comes to ISS and docks. Crew enters and performs checkout. Orion undocks. Now it really needs a space tug that can push it to Lunar Transfer Orbit. Dragon XL has IDSS docking port. Luckily, it has already been designed to be both active or passive. You know, because of Tank Dragon. But its twenty tons of fuel is not sufficient. It needs more. Much more. Like....80 tons more. Luckily, SpaceX has an alternative for that. NO, NOT STARSHIP. Something much simpler. Dragon FuelPod. Now what that would be? Take Dragon 2 trunk. You know the one with solar panels on it. Tank Dragon would have if filled with fuel, oxidizer and pressure gas tanks. Now extend it a little bit. Slap passive IDSS adapter at the back. And active IDSS adapter at the front. Then you need all these pesky GNC, batteries, attitude control stuff. But IDSS is pretty much the same as on your XL variant. You have power, comm and custom fuel transfer connectors. The good thing is you can stack these as much as you want. Ok, there must be a limit, due to imperfections due to vibrations, center of gravity etc. etc. But if they can solve it for ISS reboost, this should be simpler. Lets say that each module carries 20t of fuel and has 2t of structure. So you have Orion plus four FuelPods plus Dragon XL on the back. Powered by vacuum optimized SuperDraco. That would be the first train in space. How cool would that be. I know, rockets are not legos. But they are not designed to be legos. But ISS, in some way, is more similar to LEGO. and Lunar Gateway too. Because it is designed that way.
But I am sidetracking. This seems very complex. It replaces single SLS launch with SIX Falcon Heavy launches and one Crew launch to ISS. Also it could not perform a single burn, due to limitations of fuel transfer speed. So actual mission would require five burns distributed over five orbits due to Oberth effect causing multiple crossings of Van Allen radiation belts. With additional hardware. But these six launches would cost less than one SLS. And total additional development cost? Probably still cheaper that single SLS cost. Human launch would use ISS Crew program vehicles, used many times before first SLS launch. Which never flew before and will fly once before sending crew. That uses engines that were built....20 years ago? 30 years ago? This was backed by the same folks that thought that Antares with engines from Moon era were a good idea. And they will be using upper stage that will fly just once before? I know, it was derived from Delta IV upper stage.
Could the same train be used to launch Europa Clipper? Sure. And any other deep space mission. In essence it provides true distributed launch capability advocated by ULA. But it uses NTO/MMH that is known to be storable in satellites for decades. It has significantly lower ISP than Centaur or ACES. But it is proven, reliable, durable. Due to high density of the fuel, it will have better mass ratio then hydrolox. But its most important benefit is that it can be easily scaled to various delta-V requirements, as shown in this Orion though exercise. I would agree that this is the extreme case. For example, Dragon XL could perform staging after it empties tanks from one FuelPod and repeat a docking operation.
There is more. NASA did not yet select the partner for Artemis transfer/decent/ascent stage. We know that proposal from Blue Origin will (probably) use hydrolox which is potentially problematic for long duration storage. But what if the selected partner plans to use NTO/MMH? Not very efficient regarding ISP. But can last for years if needed. So, Dragon XL with its IDSS derived fuel transfer and FuelPod alternative could provide direct fuel transfer to Artemis stages. All done through standardized IDSS fuel transfer extension. That would be great short-term boost for Artemis capabilities. Long term, NTO/MMH cannot be easily or at all produced on the Moon or Mars. But it would provide sustainable lunar exploration arhitecture that could be funded at the present NASA funding level. Alternatively, Dragon XL could act as a transfer stage from the Gateway to LLO and back. What is lacks in ISP, it makes up in mass/fuel capacity. Plus it is essentially zero additional development cost.
This approach seems complex, but the same objection was attributed to multiple use of the same engine on the rocket stages. Falcon 9 was considered very risky approach. But looking back to it, in less than ten years, Merlin 1D became the most reliable and (re)used American rocket engine in the last decade that is quickly approaching its 100th launch. Standardization and reuse was, in many ways, the key factor that made SpaceX successful. Thus Dragon XL really has a lot of potential for reuse as space tug. So much, that it could effectively replace SLS derived architecture without depending on Starship success.
Dragon XL could have useful life even after Starship enters production. Starship/SuperHeavy is optimized for staging/refueling in LEO. For smaller payloads (such as geostationary satellites) it would provide ideal reusable LEO to GTO transfer vehicle. And it could provide ISS and LOP-G certified docking capability that might be missing for years after Starship enters operations. SO Dragon could have a lot of possible applications. But its future capabilities really depend on NASA future requirements. But Dragon XL represents iterative improvement methodology which proved very successful with Falcon family. It is not efficient and optimized. Just like Falcon was not performance optimized compared to Atlas V or Delta IV or Ariane V. And yet, Falcon 9 effectively caused all three to disappear in the next few years. Since they were so optimized to be expensive.
Even before the great success was achieved, huge cost of the undertaking made many government heads a little bit sober. This could not be sustained. But the whole development and production ecosystem was built around that. And so, as Apollo winded down, Apollo Applications Program was born. There were many great ideas foreseen in the program, of which only Skylab and Apollo/Soyuz rendezvous were realized. But in many ways, this program could be seen as a precursor of ISS.
Ever since Apollo, NASA appeared as living of the old glory. Using a "shoestring" budget compared to Apollo, it seems unable to repeat the glorious achievements of the past. Despite Voyagers, first reusable spacecraft, space telescopes, long duration Mars rovers, in-space construction and assembly, permanent 20-year manned presence in space, somehow that was not enough to match high expectations set by Apollo 11.
Every few years there is new initiative, a new vision made by presidents. Go back to the Moon. No, go to the Mars. No, lets do asteroids first. Maybe Moon again? Why not just a deep space station? But for decades, such human exploration initiatives just fall short. It just does not work. Presidents come and go. Some stay four years, some eight. The next president wants near term results. Something sexy and dramatic. In four years. And that it does not cost much. Because president does not approve the budget. And frankly, achievement seeking space program is not really worth various trade-offs that politicians need to make to get the funding.
So what gets funded? International cooperation and commitments. Once there is foreign policy commitment to some program (such as ISS or LOP-G), there is high cost of backing down. For a nation that sees itself as a global leader. Also, local politicians like to support local, aerospace industry. Especially if they don't have so much of high tech to offer (yes, I am talking about Alabama). Incremental, low risk improvements are preferred. Risk should be reduced as much as possible. Because any failure, especially loss of human life, causes multi-year delay or even program cancellation.
Will Artemis survive long-term? Will SLS be successful? Or LOP-G? Or ISS? Or Axiom commercial space station? I cannot predict the future. But for many space enthusiasts, SpaceX and Elon Musk has been a savior of space-faring future. Other programs have consistently been over budget and so expensive they could not be sustained long term. Although launch and equipment costs have decreased over the decades, due to "feature creep", push to develop and test new things in space, ever decreasing risk tolerance, there is appearance of snail-paced progress.
SpaceX has changed that paradigm. It developed low-cost rocket. It iterated it to increase trust and capacity from Falcon 9 V1.0 to latest Falcon Heavy almost ten times. It developed low cost first stage and fairing re-usability. SpaceX managed to decrease launch cost per kilogram (compared to EELV program) almost five times.
While all eyes are focused on next generation Starship development, which promises another order of magnitude cost reduction, Dragon 2 based architecture is just entering operational phase. Last year we had Demo-1 launch to ISS. Demo-2 first crewed flight is planned for May. Followed by first long term crew flight USCV-1 in August. And first Dragon 2 resupply mission in September. Three Dragon 2 missions planned just for this year. So Dragon 2 will have steady pipeline of four to six missions every year. Without other space tourist missions that might commence from next year.
Latest, a little bit lukewarm announcement was selection of Dragon XL as Lunar Gateway resupply provider. A new variant that has really scarce details. All that is known is payload mass of 5000 kg and one rendering. So why is Dragon XL a game changer for NASA and lunar exploration?
We know that Elon Musk is a big fan of re-usability. Sure, they could develop Dragon XL as a throwaway capsule much like Cygnus. Just remove unneeded head shield, change the outer mold to have more internal space and repackage existing technology. Easy money, that can be used to fund Starship and Starlink development. SpaceX should not spend a dime to go beyond and above NASA requirements. After all, Boeing will not do it. Northrop Grumman will not do it. And that is why they can slowly respond.
But the fact is, Elon Musk cannot be sure when and if Starship will be operational. Nor how much money will go down the drain. Mk1, SN1, SN2, SN3 and interim test tanks have all failed. They switch body material from Al-Li to composites to stainless steel. And God knows how many failures are awaiting with reentry and landing efforts. Not to mention life support and MMOD resiliency.
For Starlink, booster and fairing reuse have been the backup plan that enables much cheaper launch capacity, that might allow SpaceX to avoid bankruptcy. So it is clear that SpaceX is trying to pursue all funded missions possible. And that is why Dragon XL is important.
Artemis and Lunar Gateway are highly dependent upon SLS, a poster child of inefficient and bloated government program. Like a zombie, shuttle derived technology survived for half a century with just a minor changes. And it has been impossible to kill, since there was no alternative. Yes, there was distributed launch idea based on EELV/ULA. But it is not proven nor available now. And with ULAs parents, any such alternative would end up similar to SLS.
So how could one supply vehicle change this? And make SLS obsolete? Well, if Dragon XL will just be like Cygnus with IDSS port, it will not change much. SpaceX could earn good money for it, making it single purpose vehicle designed for one purpose and one purpose only. Paired with Falcon Heavy and existing propulsion and fuel capacity, it can reach the gateway. But can SpaceX do more with minor changes?
First, all vehicles coming to Lunar Gateway (with the exception of Lunar Ascent Vehicle) will not be reusable. Ok, Orion should be. Except the service module. And the heat shield. So with moderate additional deltaV, Dragon XL could perform aerobraking to LEO using Earth atmosphere. Since it is coming from cis-lunar space, there is no need for heat-shield. Even bring just 20m/s on single pass through upper atmosphere should be sufficient to aerobrake to LEO in less than six months. Yes, it will pass through Van-Allen belts many times. But it should be designed to sustain this crossing anyway.
Once in LEO, what can be done with it? Well, if SpaceX could design its docking port to be both active and passive at the same time...maybe they could launch crew dragon to LEO. Two astronauts with logs of bags, dock with Dragon XL and transfer the cargo from Crew Dragon to XL. Expendable parts? Ok, probably there is no way to cram 5000kg of bags together with two astronauts into the Crew Dragon. Maybe that is bad idea. And it might be a little bit hard to design IDSS port for both active and passive mode. But the same Dragon XL could dock to ISS. And then transfer the equipment from other supply vehicles to Dragon XL. After all, what are these space tourists going to do for days on ISS? Talking with REAL astronauts? Gazing from cupola whole day? Well...they could carry bags around. It might be easier than on Earth!
One nice thing about this approach is that if would provide cargo return capability from Lunar Gateway to the Earth. In the future, samples collected by probes and rovers from comets, Mars or Moon could be brought to Lunar Gateway first. Even analysed there. You know, planetary protection and stuff. But that is far in the future.
Once that Dragon XL is docked to ISS and fully loaded, it can undock. But there is a problem. It can have new cargo for lunar gateway. But there is no propellant to get there. It requires nearly 4km/s delta-V to get to the Lunar Gateway. Plus fuel to return back. So what Dragon XL really needs is a tank full of propellant. And a lots of it. Such a tank could be launched on separate Falcon Heavy flight.
In fully reusable configuration Falcon Heavy could launch around 28 tons to LEO. So that would be ideal mass of the tank full of MMH/NTO propellant. What should such a tank have? Well, it needs passive IDSS port so that Dragon XL can dock to it. It needs some solar panels. Maybe the same as Dragon XL, or attached around the trunk like Dragon 2. But it could reuse many systems from Dragon 2 or Dragon XL. Heck, it can even BE a special variant of Dragon 2, filled with additional MMH/NTO fuel. Its 9m3 of pressurized and 12m3 of unpressurized cargo space could be used for additional tanks. It could be designed to automatically dock with Dragon XL and transfer fuel. Assuming 21m3 of volume and propellant density of 1200kg/m3, Such Tank Dragon variant could provide at least 20 tonnes of propellant to Dragon XL. Plus, it could also dock with ISS and perform ISS reboost as needed. This could be done by single Draco thruster, similar to ISS reboost experiment done with Cygnus.
An obvious requirement for Dragon XL would be to have similarly sized tanks, that could hold 20 tons of fuel. And note that this could be a limiting factor for payload mass to gateway, highly dependent upon dry mass of Dragon XL.
How would fuel transfer be performed? IDSS standard does not specify this, but it has been foreseen as future enhancement. But the transfer is not so easy - it requires three connectors - for fuel (MMH), oxidizer (NTO) and pressure gas (He). In the spirit of androgynous docking design and two-way fuel transfer capability, it will probably be symmetric and distributed in the keep-clear zones of IDSS dock. This would be the major new capability that would require NASA clearance (and ideally funding support). But that would allow full resupply chain from Earth to ISS to Lunar gateway and back. It would require two launches (Falcon Heavy/Tank Dragon and Falcon 9/Cargo Dragon) instead of one. And additional astronaut time to transfer cargo through ISS. But the only discard-able parts of the infrastructure would be two Falcon upper stages and a single Dragon trunk.
With this capability, Cargo Dragon could also act as a space tug from GTO to GEO and back to LEO for geostationary satellites. Now all that is nice, but how could this make Dragon XL an SLS killer? After all, only SLS can launch Orion to the Gateway, right? Well...reusable Falcon Heavy can launch Orion to the ISS. Since it is not man-rated, it can launch it without crew and escape tower. Not bad. And crew can hang out and chill on the ISS, coming with the flight proven ....Starliner. Since they have nothing to do, they might transfer the cargo around. But that is not really important right now. So, Orion comes to ISS and docks. Crew enters and performs checkout. Orion undocks. Now it really needs a space tug that can push it to Lunar Transfer Orbit. Dragon XL has IDSS docking port. Luckily, it has already been designed to be both active or passive. You know, because of Tank Dragon. But its twenty tons of fuel is not sufficient. It needs more. Much more. Like....80 tons more. Luckily, SpaceX has an alternative for that. NO, NOT STARSHIP. Something much simpler. Dragon FuelPod. Now what that would be? Take Dragon 2 trunk. You know the one with solar panels on it. Tank Dragon would have if filled with fuel, oxidizer and pressure gas tanks. Now extend it a little bit. Slap passive IDSS adapter at the back. And active IDSS adapter at the front. Then you need all these pesky GNC, batteries, attitude control stuff. But IDSS is pretty much the same as on your XL variant. You have power, comm and custom fuel transfer connectors. The good thing is you can stack these as much as you want. Ok, there must be a limit, due to imperfections due to vibrations, center of gravity etc. etc. But if they can solve it for ISS reboost, this should be simpler. Lets say that each module carries 20t of fuel and has 2t of structure. So you have Orion plus four FuelPods plus Dragon XL on the back. Powered by vacuum optimized SuperDraco. That would be the first train in space. How cool would that be. I know, rockets are not legos. But they are not designed to be legos. But ISS, in some way, is more similar to LEGO. and Lunar Gateway too. Because it is designed that way.
But I am sidetracking. This seems very complex. It replaces single SLS launch with SIX Falcon Heavy launches and one Crew launch to ISS. Also it could not perform a single burn, due to limitations of fuel transfer speed. So actual mission would require five burns distributed over five orbits due to Oberth effect causing multiple crossings of Van Allen radiation belts. With additional hardware. But these six launches would cost less than one SLS. And total additional development cost? Probably still cheaper that single SLS cost. Human launch would use ISS Crew program vehicles, used many times before first SLS launch. Which never flew before and will fly once before sending crew. That uses engines that were built....20 years ago? 30 years ago? This was backed by the same folks that thought that Antares with engines from Moon era were a good idea. And they will be using upper stage that will fly just once before? I know, it was derived from Delta IV upper stage.
Could the same train be used to launch Europa Clipper? Sure. And any other deep space mission. In essence it provides true distributed launch capability advocated by ULA. But it uses NTO/MMH that is known to be storable in satellites for decades. It has significantly lower ISP than Centaur or ACES. But it is proven, reliable, durable. Due to high density of the fuel, it will have better mass ratio then hydrolox. But its most important benefit is that it can be easily scaled to various delta-V requirements, as shown in this Orion though exercise. I would agree that this is the extreme case. For example, Dragon XL could perform staging after it empties tanks from one FuelPod and repeat a docking operation.
There is more. NASA did not yet select the partner for Artemis transfer/decent/ascent stage. We know that proposal from Blue Origin will (probably) use hydrolox which is potentially problematic for long duration storage. But what if the selected partner plans to use NTO/MMH? Not very efficient regarding ISP. But can last for years if needed. So, Dragon XL with its IDSS derived fuel transfer and FuelPod alternative could provide direct fuel transfer to Artemis stages. All done through standardized IDSS fuel transfer extension. That would be great short-term boost for Artemis capabilities. Long term, NTO/MMH cannot be easily or at all produced on the Moon or Mars. But it would provide sustainable lunar exploration arhitecture that could be funded at the present NASA funding level. Alternatively, Dragon XL could act as a transfer stage from the Gateway to LLO and back. What is lacks in ISP, it makes up in mass/fuel capacity. Plus it is essentially zero additional development cost.
This approach seems complex, but the same objection was attributed to multiple use of the same engine on the rocket stages. Falcon 9 was considered very risky approach. But looking back to it, in less than ten years, Merlin 1D became the most reliable and (re)used American rocket engine in the last decade that is quickly approaching its 100th launch. Standardization and reuse was, in many ways, the key factor that made SpaceX successful. Thus Dragon XL really has a lot of potential for reuse as space tug. So much, that it could effectively replace SLS derived architecture without depending on Starship success.
Dragon XL could have useful life even after Starship enters production. Starship/SuperHeavy is optimized for staging/refueling in LEO. For smaller payloads (such as geostationary satellites) it would provide ideal reusable LEO to GTO transfer vehicle. And it could provide ISS and LOP-G certified docking capability that might be missing for years after Starship enters operations. SO Dragon could have a lot of possible applications. But its future capabilities really depend on NASA future requirements. But Dragon XL represents iterative improvement methodology which proved very successful with Falcon family. It is not efficient and optimized. Just like Falcon was not performance optimized compared to Atlas V or Delta IV or Ariane V. And yet, Falcon 9 effectively caused all three to disappear in the next few years. Since they were so optimized to be expensive.
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