H2O2 - Swiss Army Knife for BEO exploration
For deep space/long duration missions the usual propulsion suspects are H2/LOX (high ISP, but hard to prevent H2 boil-off), CH4/LOX (nice combo which addresses H2 density/boil-off problems), and NTO/hydrazine (storable, heavily used in satellites especially for attitude control).
Space shuttle stack had 60 different tanks (and a lot of different liquids in them), which is an obvious development, integration and testing nightmare. Now imagine what a typical manned deep space mission needs to have:
It seems to me that hydrogen peroxide can fulfill all of these purposes, which would reduce number of tanks considerably. For example, pass the small quantities of H2O2 over catalyst, and you get heat, water and oxygen (addressing the first three needs). It is a liquid in the similar temperature range as water, so it can used instead of water as part of the external shield providing radiation protection. Run it over catalyst in small thrusters, and you have RCS system with a very decent ISP compared to cold gas thrusters, and reliable thrust control. Use it in a fuel cell, and you have electric power source that can be used if batteries and/solar panels are not functional.
For the main propulsion and decent/ascent engines, it is suitable as LOX substitute since it works with the same hydrocarbons, and has approximately 15% lower Isp. This can me compensated with higher density (better wet/dry mass ratio), higher oxidizer/fuel ratio (again, improving wet/dry mass ratio) and higher boiling point (less insulation needed).
Oxygen can be used as pressurization gas produced by H2O2 decomposition (but just for H202 vessels). I guess most of H2O2 resistant materials would also be resistant to gaseous oxygen too. That would mean that most of the tanks would effectively be self-pressurized, because mass-ratio for H202/RP-1 combination is 7:1. Hydrocarbon fuel can be pressurized with nitrogen (which is also needed for breathing).
So, it has many advantages, where one chemical is used for many different purposes. It is liquid at room temperatures (I guess this would help with thermal management a lot), very dense, not so toxic as NTO/hydrazine combination, and has ideal decomposition byproducts.
The drawbacks are its decomposition rate (which improves with purity), lower ISP, and requires careful choice of materials which must not be decomposition catalysts (I think that would be the main problem with its usage). I suspect that it also cannot be easily produced using ISRU approach (with required purity).
Notice that there are better alternatives than H2O2 for each of the purposes listed. But instead choosing an optimal chemical for each system, sometimes it is better to have a common chemical that can be used for several purposes. Imagine Apollo 13 type of accident on a journey to Mars or back. Instead of having different systems and fuel/oxidizer for abort, attitude control and landing, system designers could use the same fuel/oxidizer tanks for all three purposes. Compare that with earlier capsules, such as Soyuz, which have completely separate systems for each task. But can it be used as monopropellant for RCS? No. Can you drink its combustion products? Hardly. The fume of H2O2 decomposition just needs to be cooled to room temperature - water vapor will become liquid, and oxygen can be ... vented or inhaled.
The real advantage of using this "oxidizer" is related to flexibility in deep space missions. For example, imagine what would happen in the "classic" architectures if there are the following problems:
- Sabatier process stops working - CO2 cannot be reprocessed to retrieve O2
- Water reprocessing system stops working - how many days can astronauts survive without fresh water?
- Solar based power supply is no longer available.
- The main propulsion system is damaged - no significant course corrections can be made, because in other systems you have limited delta-V budget
The closest help is months (or even years) away. But using a common chemical (H2O2) enables flexibility for astronauts the re-purpose its usage for long term survival needs.
If hydrogen perodixe is that good, who no major system uses it for space missions? Major reason lies in the history of rocketry. Although HTP (High Test Peroxide) was considered and tried, it was considered very unstable mainly due to required purity of tanks and fuselage, since many things act as decomposition catalyst for the HTP. Related to that was no other need for ultra-high purity HTP (90% concentration or higher) which reduce its industrial availability. And the third reason was that HTP/RP-1 is not a clear winner for any of the applications considered above. Only in case of an integrated system does this combination excel.
Since BFR and Raptor engine were announced, major development focus has shifted to CH4/O2 combination. It is easier to synthesize in ISRU, has higher ISP and similar boiling points. It is more complex for in-space long term storage due to cryogenic temperatures and boil-off. Reaction control system would be much harder due to issues for precise ignition requirements. So hydrogen peroxide is the ideal oxidizer, which will probably never be used due to its legacy.
Space shuttle stack had 60 different tanks (and a lot of different liquids in them), which is an obvious development, integration and testing nightmare. Now imagine what a typical manned deep space mission needs to have:
- oxygen for breathing
- drinking water
- heating and cooling
- radiation shield (ideally external shield filled with some liquid)
- attitude control thrusters
- EVA/space suite consumables
- main propulsion for orbital and injection maneuvers
- landing and ascent propulsion
- pressurization gas
- backup electric power source
It seems to me that hydrogen peroxide can fulfill all of these purposes, which would reduce number of tanks considerably. For example, pass the small quantities of H2O2 over catalyst, and you get heat, water and oxygen (addressing the first three needs). It is a liquid in the similar temperature range as water, so it can used instead of water as part of the external shield providing radiation protection. Run it over catalyst in small thrusters, and you have RCS system with a very decent ISP compared to cold gas thrusters, and reliable thrust control. Use it in a fuel cell, and you have electric power source that can be used if batteries and/solar panels are not functional.
For the main propulsion and decent/ascent engines, it is suitable as LOX substitute since it works with the same hydrocarbons, and has approximately 15% lower Isp. This can me compensated with higher density (better wet/dry mass ratio), higher oxidizer/fuel ratio (again, improving wet/dry mass ratio) and higher boiling point (less insulation needed).
Oxygen can be used as pressurization gas produced by H2O2 decomposition (but just for H202 vessels). I guess most of H2O2 resistant materials would also be resistant to gaseous oxygen too. That would mean that most of the tanks would effectively be self-pressurized, because mass-ratio for H202/RP-1 combination is 7:1. Hydrocarbon fuel can be pressurized with nitrogen (which is also needed for breathing).
So, it has many advantages, where one chemical is used for many different purposes. It is liquid at room temperatures (I guess this would help with thermal management a lot), very dense, not so toxic as NTO/hydrazine combination, and has ideal decomposition byproducts.
The drawbacks are its decomposition rate (which improves with purity), lower ISP, and requires careful choice of materials which must not be decomposition catalysts (I think that would be the main problem with its usage). I suspect that it also cannot be easily produced using ISRU approach (with required purity).
Notice that there are better alternatives than H2O2 for each of the purposes listed. But instead choosing an optimal chemical for each system, sometimes it is better to have a common chemical that can be used for several purposes. Imagine Apollo 13 type of accident on a journey to Mars or back. Instead of having different systems and fuel/oxidizer for abort, attitude control and landing, system designers could use the same fuel/oxidizer tanks for all three purposes. Compare that with earlier capsules, such as Soyuz, which have completely separate systems for each task. But can it be used as monopropellant for RCS? No. Can you drink its combustion products? Hardly. The fume of H2O2 decomposition just needs to be cooled to room temperature - water vapor will become liquid, and oxygen can be ... vented or inhaled.
The real advantage of using this "oxidizer" is related to flexibility in deep space missions. For example, imagine what would happen in the "classic" architectures if there are the following problems:
- Sabatier process stops working - CO2 cannot be reprocessed to retrieve O2
- Water reprocessing system stops working - how many days can astronauts survive without fresh water?
- Solar based power supply is no longer available.
- The main propulsion system is damaged - no significant course corrections can be made, because in other systems you have limited delta-V budget
The closest help is months (or even years) away. But using a common chemical (H2O2) enables flexibility for astronauts the re-purpose its usage for long term survival needs.
Since BFR and Raptor engine were announced, major development focus has shifted to CH4/O2 combination. It is easier to synthesize in ISRU, has higher ISP and similar boiling points. It is more complex for in-space long term storage due to cryogenic temperatures and boil-off. Reaction control system would be much harder due to issues for precise ignition requirements. So hydrogen peroxide is the ideal oxidizer, which will probably never be used due to its legacy.
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