I have not read or heard a lot about the steering thrusters of BFR. They are a new type of engine in their own right with its own development project, control and fuel supply. The list below is from memory and I would love to update them to something more substantial.
What we know:
* Methane/Oxygen fuel
What we assume:
* Pressure fed
* gas-gas combustion
What we dont know:
* max/min thrust
* ISP
* mass
* reaction time (important since they should be used for attitude control)
We know some of these.
It's been stated landing in 60KM/H winds is OK. Elon on twitter (https://mobile.twitter.com/elonmusk/status/1015654917782978560?lang=en)
This allows you to come up with a figure close to 15 tons/axis for BFS, somewhat more for BFR (to cancel the wind velocity and land vertically with no gimbal)
This more or less works with the observed thruster diameters on IAC2017 model - I have not gone over the 2018 images looking for them.
Min thrust of a gas thruster can be very low, if you operate it in cold gas mode, plus, the whole reason for going gas/gas was 'minimum impulse bit'. Elon on Reddit (https://www.reddit.com/r/space/comments/76e79c/i_am_elon_musk_ask_me_anything_about_bfr/dodfh6x/)
If the thrusters are a little more powerful than this, 30 tons - they enable lunar landing and takeoff with enough fuel to ascend (50t) and a minimal payload, and perhaps even land horizontally.
Have they thought of this and realised it would be handy - who knows.
Oversizing them this way from the 15 tons calculated above for 60km/h to 60MPH winds would considerably improve ability to ignore most winds.
I have not read or heard a lot about the steering thrusters of BFR. They are a new type of engine in their own right with its own development project, control and fuel supply. The list below is from memory and I would love to update them to something more substantial.
What we know:
* Methane/Oxygen fuel
What we assume:
* Pressure fed
* gas-gas combustion
What we dont know:
* max/min thrust
* ISP
* mass
* reaction time (important since they should be used for attitude control)
We know some of these.
It's been stated landing in 60KM/H winds is OK. Elon on twitter (https://mobile.twitter.com/elonmusk/status/1015654917782978560?lang=en)
This allows you to come up with a figure close to 15 tons/axis for BFS, somewhat more for BFR (to cancel the wind velocity and land vertically with no gimbal)
This more or less works with the observed thruster diameters on IAC2017 model - I have not gone over the 2018 images looking for them.
Min thrust of a gas thruster can be very low, if you operate it in cold gas mode, plus, the whole reason for going gas/gas was 'minimum impulse bit'. Elon on Reddit (https://www.reddit.com/r/space/comments/76e79c/i_am_elon_musk_ask_me_anything_about_bfr/dodfh6x/)
If the thrusters are a little more powerful than this, 30 tons - they enable lunar landing and takeoff with enough fuel to ascend (50t) and a minimal payload, and perhaps even land horizontally.
Have they thought of this and realised it would be handy - who knows.
Oversizing them this way from the 15 tons calculated above for 60km/h to 60MPH winds would considerably improve ability to ignore most winds.
Reading to this thread brings up a question. These gas- gas thrusters would seem to be relatively easy to build. So my question is, could you modify the Raptor engines to have a gas-gas mode and would it be useful? I know the efficiencies would be much lower, what I'm thinking of is giving you more finesse / control especially in lower gravity Landings.
The BFS will have methalox RCS thrusters for spaceship attitude control. (See the three dark dots at the bottom of the spaceship.)
>
The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).
Elon Musk, Reddit AMA
https://www.reddit.com/r/space/comments/76e79c/i_am_elon_musk_ask_me_anything_about_bfr/QuoteThe BFS will have methalox RCS thrusters for spaceship attitude control. (See the three dark dots at the bottom of the spaceship.)
>
The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).
The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).
Yes. All-weather. ~300km/h high altitude winds. ~60km/h ground winds. It’s a beast.
~3 bar - 45PSI.
There already is a gas generator system, autogenius pressurization if the main tanks.
What pressure is that, and can it be tapped to fuel the thrusters?
One reason to consider the lower altitude a limiting is you have less time to react.I was assuming it in the original post, as there is a _long_ phase from 20km down where you can correct for errors over a long period, and then be prepared to light the main engine with some error that needs correcting.
This is the tank pressure, what about the pressure in the system that is pressurizing the tank?~3 bar - 45PSI.
There already is a gas generator system, autogenius pressurization if the main tanks.
What pressure is that, and can it be tapped to fuel the thrusters?
So probably not very useful.
Is oxygen gas now considered lox? :'(No, it's gox.
If the thrusters are a little more powerful than this, 30 tons - they enable lunar landing and takeoff with enough fuel to ascend (50t) and a minimal payload, and perhaps even land horizontally.
Have they thought of this and realised it would be handy - who knows.
Oversizing them this way from the 15 tons calculated above for 60km/h to 60MPH winds would considerably improve ability to ignore most winds.
Thread title is wrong now.
They are methox (gas - gas) thusters, not methalox.
Musk even called them methox in that interview with Tim Dodd. And said they'd be of pressure fed type.
There is no LOX in the Starship thrusters.
Years ago my team worked on a rechargeable gaseous RCS system. It had 1000 psi tanks ofgaseous LoxGOX and CH4. As the gases were used the pressure and temperature of the gases go down. When the tank pressure dropped below a set limit, an electric pump and heater were used to to pump liquid and gasify propellants from the main tanks into the RCS tanks. As long as you had liquid propellants and electrical power, you could maintain your high pressure gaseous system. It could even be completely offline for years and be recharged before launch from Mars or the Moon.
RCS and OMS are probably going to both be gaseous CH4/GOX because they need to both operate in zero g, and operate instantaneously. It will probably be an integrated RCS/OMS system.
I think they will make use of a lot of the tech they developed for draco/superdraco. Very similar requirements from a pressurization, plumbing perspective. Biggest difference is the need for fail safe ignition, since CH4/GOX is not hypergolic. I would expect to see redundant ignition systems in each rocket as well as redundant rockets. 2 OMS, ~12 RCS.
Fantastic, someone who worked on a similar system! :) May I ask some questions?
* How powerful were your thrusters?
* How big was the reservoir/how long could you sustain using it? Say, in cumulative thruster firing seconds at full thrust?
* What was the responds time and thrust resolution?
* Did you go for throttle or pulse to control impulse?
I would guess, when they 'arm' the RCS system, a small sustained torch goes on in all the thrusters using spark ignition for a sustained flame. Then they only need to feed gaseous CH4 and O2 into the combustion chamber. The torches will use some small amount of fuel, but the hot RCS system only needs to be on for a few minutes during reentry, so its not a big loss in terms of mass.
I assume the same thruster could work as a cold gas thruster for in-space maneuvering using CH4 only. This could be used to align the Starship engines with the sun or during precision maneuvering like docking. Not sure if the hot fire mode would be precise enough for these.
For docking you need pointing and translation, so I guess there must be at least 2 reservoirs each for CH4 and O2, one set in the nose of Starship and one at the bottom.
This is the tank pressure, what about the pressure in the system that is pressurizing the tank?~3 bar - 45PSI.
There already is a gas generator system, autogenius pressurization of the main tanks.
What pressure is that, and can it be tapped to fuel the thrusters?
So probably not very useful.
Might this be used to pressurize a seperate tank to a higher pressure?
Years ago my team worked on a rechargeable gaseous RCS system. It had 1000 psi tanks ofgaseous LoxGOX and CH4. As the gases were used the pressure and temperature of the gases go down. When the tank pressure dropped below a set limit, an electric pump and heater were used to to pump liquid and gasify propellants from the main tanks into the RCS tanks. As long as you had liquid propellants and electrical power, you could maintain your high pressure gaseous system. It could even be completely offline for years and be recharged before launch from Mars or the Moon.
The problem with any sort of pump from the main tanks into the RCS tanks is that most of the RCS usage will be in a short period during landing. Out in space, they can afford to maneuver with a little puff of RCS and it's not a big deal if it takes 5 minutes for the vehicle to slowly turn around to the direction they want it in. This is even true with docking since you can just move very slowly.
However, this does not hold for atmospheric control. In this case, you have to overcome aerodynamic resistance to maneuvering, meaning the thrusters have to exert a lot of force for a more sustained period, and thus you burn a lot of fuel. Remember, this phase of flight is very short, with the bulk of the maneuvering needing RCS happening in the last seconds transitioning from belly flop to vertical landing. In order for pumps to work, they would need to keep up with the thrusters, so you would have to vaporize on the order of 10s to 100s of kgs of fuel per second, which takes a huge amount of power.
To put things in perspective, 1 kW will vaporize 1 gram of methane every 5 seconds. But if the assumption about the bulk of RCS fuel being used in less than 5 seconds to perform the horizontal-vertical transition we need many thousands of times higher rate if we want an under provisioned pressurized tank! Probably less that a gigawatt, but certainly quite a few megawatts...
It's very hard to imagine the components needed to produce and transfer this sort of wattage being lighter than just using a bigger pressure vessel.
To put things in perspective, 1 kW will vaporize 1 gram of methane every 5 seconds.Trivial correction: 1 kW will vaporize TEN grams in 5 seconds, you slipped a digit.
So given the high wattage necessary for vaporization. A preburner with no turbine but just enough O2 or CH4 to vaporize the fuel/oxidizer. It seems that they would be very simple?could you run the LOX or LCH4 in separate cooling loops on the nozzle to cool it, vaporize them and maintain tank pressure during longer burns? Just a guess.... Perhaps only have a small local tank, almost part of each thruster where the liquids are flashed to gas as they are needed! thus LOX and LCH4 are piped to the engine, and only for the first seconds is electric heating needed, then the flashing is done by the nozzle! Electric pumps would still need to pump the liquids at high pressure. (a la Electron rocket)
So given the high wattage necessary for vaporization. A preburner with no turbine but just enough O2 or CH4 to vaporize the fuel/oxidizer. It seems that they would be very simple?
Here is a simplified schematic of a rechargeable RCS / OMS system:
- LCH4 and LOX comes from header tanks.
- electric pumps pump in liquids and heaters gasify to maintain pressures above set lower limit.
- electric heaters maintain desired temperature range.
- A coolant loop could be added to reduce electrical needs by transferring heat from thrusters back to the RCS tanks.
John
Here is a simplified schematic of a rechargeable RCS / OMS system:
- LCH4 and LOX comes from header tanks.
- electric pumps pump in liquids and heaters gasify to maintain pressures above set lower limit.
- electric heaters maintain desired temperature range.
- A coolant loop could be added to reduce electrical needs by transferring heat from thrusters back to the RCS tanks.
John
Does this system also produce the 3 Bar for the tanks? If not, what does? We don’t want to need helium or nitrogen.
Something on Mars will have to press the tanks before launch. That can’t be the raptors. Though they can keep the tanks pressed during their burn.
I've seen diagrams both ways... the RCS tanks can store the mixed gas right?
How severe is the mass penalty for multiple small tanks over monolithic large tanks?The added failure modes will likely make this sort of system *less* reliable than a simpler system.
I'm wondering about reduncancy, and whether it would be worth giving individual RCS blocks their own pressure vessels. Replenished from a central source, but with fuel on hand if the central source fails.
How severe is the mass penalty for multiple small tanks over monolithic large tanks?
I'm wondering about redundancy, and whether it would be worth giving individual RCS blocks their own pressure vessels. Replenished from a central source, but with fuel on hand if the central source fails.
I've seen diagrams both ways... the RCS tanks can store the mixed gas right?
You mean mixed gas and liquid? As a mixture of oxygen and methane at high pressure is not going to stay at that pressure for long.
I've seen diagrams both ways... the RCS tanks can store the mixed gas right?
You mean mixed gas and liquid? As a mixture of oxygen and methane at high pressure is not going to stay at that pressure for long.
Sorry I was clear... they will be extracting from the LOX and LCH4 header tanks into a new GOX and GCH4 RCS tanks.
Can that new (GOX and GCH4) be a single tank?
I've seen diagrams both ways... the RCS tanks can store the mixed gas right?
You mean mixed gas and liquid? As a mixture of oxygen and methane at high pressure is not going to stay at that pressure for long.
Sorry I was clear... they will be extracting from the LOX and LCH4 header tanks into a new GOX and GCH4 RCS tanks.
Can that new (GOX and GCH4) be a single tank?
If I saw this config I would never ride on the thing even if paid. When you mix GOX and GCH4...or any oxidizer and fuel.....you get a bomb, plain and simple.
I state this with certainty...you will never see a single tank with both in it.
I've seen diagrams both ways... the RCS tanks can store the mixed gas right?
You mean mixed gas and liquid? As a mixture of oxygen and methane at high pressure is not going to stay at that pressure for long.
Sorry I was clear... they will be extracting from the LOX and LCH4 header tanks into a new GOX and GCH4 RCS tanks.
Can that new (GOX and GCH4) be a single tank?
If I saw this config I would never ride on the thing even if paid. When you mix GOX and GCH4...or any oxidizer and fuel.....you get a bomb, plain and simple.
I state this with certainty...you will never see a single tank with both in it.
I understand that argument but there is no ignition source.
Automobile gasoline tanks have air and gaseous gasoline in them.
which makes it 3*10^5 kW of power
that's 30 Megawatt.
I've seen diagrams both ways... the RCS tanks can store the mixed gas right?,
You mean mixed gas and liquid? As a mixture of oxygen and methane at high pressure is not going to stay at that pressure for long.
Sorry I was clear... they will be extracting from the LOX and LCH4 header tanks into a new GOX and GCH4 RCS tanks.
Can that new (GOX and GCH4) be a single tank?
If I saw this config I would never ride on the thing even if paid. When you mix GOX and GCH4...or any oxidizer and fuel.....you get a bomb, plain and simple.
I state this with certainty...you will never see a single tank with both in it.
I understand that argument but there is no ignition source.
Automobile gasoline tanks have air and gaseous gasoline in them.
I've seen diagrams both ways... the RCS tanks can store the mixed gas right?,
You mean mixed gas and liquid? As a mixture of oxygen and methane at high pressure is not going to stay at that pressure for long.
Sorry I was clear... they will be extracting from the LOX and LCH4 header tanks into a new GOX and GCH4 RCS tanks.
Can that new (GOX and GCH4) be a single tank?
If I saw this config I would never ride on the thing even if paid. When you mix GOX and GCH4...or any oxidizer and fuel.....you get a bomb, plain and simple.
I state this with certainty...you will never see a single tank with both in it.
I understand that argument but there is no ignition source.
Automobile gasoline tanks have air and gaseous gasoline in them.
Were you around for the discussion of obscure ignition sources for the composite overwrapped pressure vessels (COPV's) submerged in liquid oxygen! This was after the SpaceX on pad explosion.
Apologies for not having a link, but a lot of knowledgable people agreed that there will always be an ignition source.
All quiet on the hot-gas RCS front? The plan back at the Mk.1 unveil was for Mk.1 & 2 to use cold-gas RCS only, with hot-gas RCS added to Mk.3. Obviously with the switch to the SN series that timeline is no longer valid, but if hot-gas RCS is as imminent as it was previously going to be we should be seeing some evidence of component testing.The could be heavily into testing hot gas thrusters ... how would we know? I'd expect most of the test campaign to happen in McGregor, and these things will be so tiny compared to things like Raptor, or even Merlin, that I doubt anyone would even notice. I expect the first sign of hot gas RCS at BC will be when they install RCS packs that look different from what came before, and barring any tweets from Elon, we won't really know until they light them off for the first time.
Did this a while back. Notional schematic of gaseous RCS system.
Did this a while back. Notional schematic of gaseous RCS system.
I assume the pumps, etc, will be able to operate in microgravity. How do you avoid the possibility of feeding them gas instead of liquid, or is that not an issue?
Musk has talked about hot methalox RCS before for landing Starship and suggested that they needed to be pretty hefty, seems like it's plausible this could be those or an evolution of those, especially if they're something already in the pipe.
I think he said the methalox RCS would share injector design heritage with the SuperDraco but be fed with methane and oxygen. I wonder if it would be practical to use gas-fed for these the way the RCS was described, though, seems like it could be a real challenge to generate that much gaseous methane and oxygen for a burn of more than a couple seconds at this scale, so maybe these can re-use Raptor injectors (with gas-pressurized delivery, that would have a lesser requirement on pressurization than burning the gaseous LH2 & O2 directly, right?)
Please use previous thread: https://forum.nasaspaceflight.com/index.php?topic=46574.0
Please use previous thread: https://forum.nasaspaceflight.com/index.php?topic=46574.0
I'm not discussing the RCS system. These engines are, to me, clearly a separate system even if there may be some overlap in function and design.
The difference between these and the RCS is like the difference between Draco system and the SuperDracos on Dragon.
From the thread you are not discussing:Please use previous thread: https://forum.nasaspaceflight.com/index.php?topic=46574.0
I'm not discussing the RCS system. These engines are, to me, clearly a separate system even if there may be some overlap in function and design.
The difference between these and the RCS is like the difference between Draco system and the SuperDracos on Dragon.
For those who have L2 access......there's a REASON we use old threads when possible.
(those that don't, this should block you (link will not work)... click and pic will download to your pc (for me anyway))
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=47345.0;attach=1628795;sess=45275
Notice... the following in this pic...
The huge horizontal gas bottle 'farm' (in two parts) behind the small motor test cell behind the two Raptor cells...
The small 'plumage' as it's called between the two gas dump pipes on the small motor cell... (compare with the Raptor 'plumage')
(Note - 'plumage' is ScaryDare's name for for what happens when you fire a rocket engine horizontally over the Texas bare ground)
Now, look at livingjw's post up above...
https://forum.nasaspaceflight.com/index.php?topic=46574.msg2062890#msg2062890
I see a ground-based version of THAT in this pic... IMHO
My guess... the gas/gas Methox thruster like noted in the recent Moon lander version has been in the works for some time now.
JA ;)
Please use previous thread: https://forum.nasaspaceflight.com/index.php?topic=46574.0
I'm not discussing the RCS system. These engines are, to me, clearly a separate system even if there may be some overlap in function and design.
The difference between these and the RCS is like the difference between Draco system and the SuperDracos on Dragon.
This seems like a faulty premise. If we think the RCS thrusters are approximately 10-ton thrust, why would that be insufficiently powerful for lunar landing using about 9 of them? Gaseous propellant storage and delivery might be an additional challenge given the duty cycle for the landing thrusters, but they seem to be same thruster design as used for RCS.
My guess... is SpaceX has developed FOUR sizes of Methane and Oxygen rocket engines... ???"It takes 10 years to design and build a new rocket engine."
Small and tuned for very fast pulsing like action... 3kN as per above post...
Medium and tuned to be throttled or pulsed... 30kN as per envy887 post...
And this Moon landing class, Large as being discussed here in this thread... est is 100kN...
These are Throttle only my guess... and MAY be liquid fed once started, to avoid a large gas storage issue...
SO... could you make a rocket engine that starts on gas/gas and throttles into a liquid/liquid source?
Sure... It's a mini Raptor... :o
OR not... :-\
On edit... SO
3 kN (SS/SL RCS thruster) speculated
30 kN (crosswind landing SS/SL thruster) speculated
100 kN (Moon landing engine (name TBD)) ----- > And subject of THIS thread...
900 kN (Merlin) old school KeroLox workhorse
2000 kN (Raptor) FFSC and state of the art IMHO
How's that for a family of engines under the SpaceX brand... 8)
My guess... ;)
My guess... is SpaceX has developed FOUR sizes of Methane and Oxygen rocket engines... ???"It takes 10 years to design and build a new rocket engine."
Small and tuned for very fast pulsing like action... 3kN as per above post...
Medium and tuned to be throttled or pulsed... 30kN as per envy887 post...
And this Moon landing class, Large as being discussed here in this thread... est is 100kN...
These are Throttle only my guess... and MAY be liquid fed once started, to avoid a large gas storage issue...
SO... could you make a rocket engine that starts on gas/gas and throttles into a liquid/liquid source?
Sure... It's a mini Raptor... :o
OR not... :-\
On edit... SO
3 kN (SS/SL RCS thruster) speculated
30 kN (crosswind landing SS/SL thruster) speculated
100 kN (Moon landing engine (name TBD)) ----- > And subject of THIS thread...
900 kN (Merlin) old school KeroLox workhorse
2000 kN (Raptor) FFSC and state of the art IMHO
How's that for a family of engines under the SpaceX brand... 8)
My guess... ;)
as late as 6 years ago, the plan was for a 12m booster to land on the launch mount in potentially heavy winds. I would believe that the RCS designed for that role would be approaching maturity around now, and while technically overpowered for Starship, it's ready.
Could you make a rocket engine that is gas/gas at its core but MAYBE also fed liquid/liquid using electric high-pressure pumps?
Starts on gas/gas and is then fed liquid through chamber and nozzle wall heat exchangers to, in effect, supercharge the 30 KN engine to 100 kN?
Could you make a rocket engine that is gas/gas at its core but MAYBE also fed liquid/liquid using electric high-pressure pumps?
Starts on gas/gas and is then fed liquid through chamber and nozzle wall heat exchangers to, in effect, supercharge the 30 KN engine to 100 kN?
raptor main combustion chamber is gasgas
Could you make a rocket engine that is gas/gas at its core but MAYBE also fed liquid/liquid using electric high-pressure pumps?
...SpaceX's proposed propulsion system is notably complex and comprised of likewise complex inividual subsystems that have yet to be developed, tested, and certified with very little schedule margin to accommodate delays. One notable example of this issue concerns SpaceX’s proposed reaction control system (RCS), which is very complex when compared to flight-proven systems and will require considerable development time. Additionally, there is significant risk associated with successful development of the integrated propulsion system given the proposed approach for integrating and testing the individual elements of the system. While I note that SpaceX has proposed a robust and aggressive plan for early systems demonstrations, which lends credibility to its proposed execution, this plan does not adequately address the risk of potential delay in development, as well as concomitant delay to SpaceX’s demonstration mission.
Could you make a rocket engine that is gas/gas at its core but MAYBE also fed liquid/liquid using electric high-pressure pumps?
Starts on gas/gas and is then fed liquid through chamber and nozzle wall heat exchangers to, in effect, supercharge the 30 KN engine to 100 kN?
raptor main combustion chamber is gasgas
Musk has talked about hot methalox RCS before for landing Starship and suggested that they needed to be pretty hefty, seems like it's plausible this could be those or an evolution of those, especially if they're something already in the pipe.
I think he said the methalox RCS would share injector design heritage with the SuperDraco but be fed with methane and oxygen. I wonder if it would be practical to use gas-fed for these the way the RCS was described, though, seems like it could be a real challenge to generate that much gaseous methane and oxygen for a burn of more than a couple seconds at this scale, so maybe these can re-use Raptor injectors (with gas-pressurized delivery, that would have a lesser requirement on pressurization than burning the gaseous LH2 & O2 directly, right?)
We're pretty sure the hot RCS are gas-gas engines, which makes the SuperDraco liquid-liquid design almost useless as a starting point. At minimum the injector and cooling would need to be completely redesigned for gas-gas, and with adding spark ignition that basically makes it a whole new engine. Which is why Musk said the RCS thrusters would be more similar to Raptor than to SuperDraco, because Raptor injects both propellants to the MCC as gases.
The landing engines could be gas-gas, but these are much more powerful than RCS in terms of thrust and total impulse so the gas storage requirements get intense. They would need a volume equal to 30 or more Falcon COPVs to hold the propellants, while with liquid propellants they would need 1/10th that volume. Since tank mass scales with volume, this could be a significant mass optimization.
- I think the tanks can be fit around the top of the LOx tank.
- I think the tanks can be fit around the top of the LOx tank.
Isn't LOX tank integral with LCH4 tank?
Or is there reason to expect some useful space around LCH4 tank, between nozzles?
- I think the tanks can be fit around the top of the LOx tank.
Isn't LOX tank integral with LCH4 tank?
Or is there reason to expect some useful space around LCH4 tank, between nozzles?
I think we should make Elon move the LOX tank back on top so we stop making this mistake.! :)
ARRRG! I did it myself! I meant the main CH4 tank. Thanks.
John
This is a thread specifically to discuss the landing engines SpaceX appears to have added for the lunar version of Starship. I'd like to consider their size, power, cycle, type, relation to other SpaceX engines, or to other companies' engines.
I'l start with my observations from the renders:
- There are 9 engines, mounted in 3 triple clusters
- The nozzle exit diameter is about 80-100 cm
- The engines are canted out about 25-30 degrees from vertical
- The need to hover a 200-400 t Starship in lunar gravity suggests about 80 to 100 kN thrust each - between SuperDraco and RL-10 in thrust.
- The plume color suggests they are not NTO/MMH and are methalox (maybe hydrolox, but with SpaceX that's unlikely).
Are they likely to be gas-gas methalox at this large size? How would the plumbing be set up and where would the prop storage be? How would they be pressurized? If they are liquid, pumped or pressure-fed? And how long would it take SpaceX to develop a new small liquid engine?
If pressure-fed liquid-liquid, could they be SuperDracos modified for cryo methane regen cooling and spark ignition?
Would it be less complicated plumbing to feed the landing engines from the header tanks? Maybe not as the LOX header is much nearer the nose than are the landing engines.
What about the previous, abandoned sub-scale version of the Raptors?
I wonder how difficult it would be to make a new version of a Methalox Super Draco, with nozzle extensions?
are we sure they not using the super dracos?
So a liquid methalox landing engine? Not a huge development, but not small either, just for the last tens of meters of lunar landing, isn't it a bit wasteful?these would be the rocket engines designed as the ITS boosters landing RCS, back when was planned to land on the launch mount in high winds. It takes 10 years to build a rocket engine after all. A bit oversized for starship's own RCS, but if it's scales, the RCS could be smaller than planned while the landing thrusters could be bigger than planned.
Do we expect this engine will have other uses? Will it be used on Mars landing too?
Could they speed up the development by reusing some stuff from Raptor? Could Raptor be down-scaled easily to create a mini-Raptor for this?
Could this engine share commonality with smaller RCS engines?
So a liquid methalox landing engine? Not a huge development, but not small either, just for the last tens of meters of lunar landing, isn't it a bit wasteful?these would be the rocket engines designed as the ITS boosters landing RCS, back when was planned to land on the launch mount in high winds. It takes 10 years to build a rocket engine after all. A bit oversized for starship's own RCS, but if it's scales, the RCS could be smaller than planned while the landing thrusters could be bigger than planned.
Do we expect this engine will have other uses? Will it be used on Mars landing too?
Could they speed up the development by reusing some stuff from Raptor? Could Raptor be down-scaled easily to create a mini-Raptor for this?
Could this engine share commonality with smaller RCS engines?
If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
What about the previous, abandoned sub-scale version of the Raptors?
these would be the rocket engines designed as the ITS boosters landing RCS, back when was planned to land on the launch mount in high winds. It takes 10 years to build a rocket engine after all. A bit oversized for starship's own RCS, but if it's scales, the RCS could be smaller than planned while the landing thrusters could be bigger than planned.Merlin was flying less than 5 years after it was a vague idea. And I'm pretty sure SpaceX is a little better staffed and equipped than Tom Mueller's garage was 19 years ago.
I was trying to get my head around how all this would work, in terms of tanking, for all the different engines. You've got the Raptors (pump-fed liquid), the RCS (pressure-fed gas) and now the soft-landers (pressure-fed liquid), all using methane and oxygen, right? All three are presumably in use during moon landings. And you need to keep it all in the correct state and pressure for when it's needed.If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
Does SuperDraco use a pintle injector?If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
are we sure they not using the super dracos?
I think it is quite unlikely. SuperDraco uses hypergolic propellants, so you would need some way of filling that up as well, not just methane and oxygen.
The current incarnation of SuperDraco is also single-use, ever since they replaced a valve with a burst disc after the Dragon 2 explosion.
why not to use common high pressure LOx and LCh4 tanks for RCS and landing trusters and to pump them up with some special pump when needed? Why RCS trusters have to be gas gas per se? Power flexibility can be resolved by the mixing ratios to some degree, and injectors are infinitely accurate (with earth G applied at least). I am completely out of my woods here :D.If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
That's assuming 100 kN engines. They don't need 9 x 100 kN to land on the Moon, even with cosine losses. 5 would do. However, 9 is just under the minimum to land a 250 t SS on Mars. If that's the plan, I expect they may actually be about 120 kN or slightly more. Or that they plan to increase the thrust later. If not, the engines may be just 70 kN to allow for 2-engine out.
why not to use common high pressure LOx and LCh4 tanks for RCS and landing trusters and to pump them up with some special pump when needed? Why RCS trusters have to be gas gas per se? Power flexibility can be resolved by the mixing ratios to some degree, and injectors are infinitely accurate (with earth G applied at least). I am completely out of my woods here :D.If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
So why have the soft landing engines use liquid/liquid, if there are perfectly functional gas/gas engines with gas/gas tankage already installed and ready to go?why not to use common high pressure LOx and LCh4 tanks for RCS and landing trusters and to pump them up with some special pump when needed? Why RCS trusters have to be gas gas per se? Power flexibility can be resolved by the mixing ratios to some degree, and injectors are infinitely accurate (with earth G applied at least). I am completely out of my woods here :D.If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
gas gas makes it possible to fire up fast in any orientation and acceleration.
livingjw showed a electric pump to supply liquids to replenish the 30bar(50bar?) gas storage.
Also heaters to vaporize?
So why have the soft landing engines use liquid/liquid, if there are perfectly functional gas/gas engines with gas/gas tankage already installed and ready to go?I'm so far from an expert that its laughable, but my limited understanding is that gas-fed engines are limited in the rate at which you can get the fuel into the engines, so are only suitable for low thrust uses like RCS. Pressure-fed liquid can shift more fuel to get more thrust, but not as much as pump-fed liquid.
Two engine types (Raptor and... I guess Harrier?), three sets of tanks (main/header/high pressure gas from raptor) instead of 3 engine types (raptor, harrier and RCS) and 4 sets of tanks.
So why have the soft landing engines use liquid/liquid, if there are perfectly functional gas/gas engines with gas/gas tankage already installed and ready to go?why not to use common high pressure LOx and LCh4 tanks for RCS and landing trusters and to pump them up with some special pump when needed? Why RCS trusters have to be gas gas per se? Power flexibility can be resolved by the mixing ratios to some degree, and injectors are infinitely accurate (with earth G applied at least). I am completely out of my woods here :D.If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
gas gas makes it possible to fire up fast in any orientation and acceleration.
livingjw showed a electric pump to supply liquids to replenish the 30bar(50bar?) gas storage.
Also heaters to vaporize?
Two engine types (Raptor and... I guess Harrier?), three sets of tanks (main/header/high pressure gas from raptor) instead of 3 engine types (raptor, harrier and RCS) and 4 sets of tanks.
So why have the soft landing engines use liquid/liquid, if there are perfectly functional gas/gas engines with gas/gas tankage already installed and ready to go?why not to use common high pressure LOx and LCh4 tanks for RCS and landing trusters and to pump them up with some special pump when needed? Why RCS trusters have to be gas gas per se? Power flexibility can be resolved by the mixing ratios to some degree, and injectors are infinitely accurate (with earth G applied at least). I am completely out of my woods here :D.If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
gas gas makes it possible to fire up fast in any orientation and acceleration.
livingjw showed a electric pump to supply liquids to replenish the 30bar(50bar?) gas storage.
Also heaters to vaporize?
Two engine types (Raptor and... I guess Harrier?), three sets of tanks (main/header/high pressure gas from raptor) instead of 3 engine types (raptor, harrier and RCS) and 4 sets of tanks.
- Whether they will be gas or liquid fed will depend on how much delta V is required for soft landing maneuver versus worst case RCS maneuvering sequence.
- If they are close then it would make sense to just use gas fed rockets, but I suspect that the delta V requirements for the soft landing will be much greater. If they are, then liquid fed rockets in order to save tankage weight.Tank weight is proportional to volume, pressure and density. Liquids are denser than gases so lighter tanks.
- I am cutting numbers now for an integrated RCS / soft landing system. I will do it both ways and see which is lighter and by how much.
John
So why have the soft landing engines use liquid/liquid, if there are perfectly functional gas/gas engines with gas/gas tankage already installed and ready to go?why not to use common high pressure LOx and LCh4 tanks for RCS and landing trusters and to pump them up with some special pump when needed? Why RCS trusters have to be gas gas per se? Power flexibility can be resolved by the mixing ratios to some degree, and injectors are infinitely accurate (with earth G applied at least). I am completely out of my woods here :D.If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
gas gas makes it possible to fire up fast in any orientation and acceleration.
livingjw showed a electric pump to supply liquids to replenish the 30bar(50bar?) gas storage.
Also heaters to vaporize?
Two engine types (Raptor and... I guess Harrier?), three sets of tanks (main/header/high pressure gas from raptor) instead of 3 engine types (raptor, harrier and RCS) and 4 sets of tanks.
- Whether they will be gas or liquid fed will depend on how much delta V is required for soft landing maneuver versus worst case RCS maneuvering sequence.
- If they are close then it would make sense to just use gas fed rockets, but I suspect that the delta V requirements for the soft landing will be much greater. If they are, then liquid fed rockets in order to save tankage weight.Tank weight is proportional to volume, pressure and density. Liquids are denser than gases so lighter tanks.
- I am cutting numbers now for an integrated RCS / soft landing system. I will do it both ways and see which is lighter and by how much.
John
One of the previous arguments was that the gas would be depleted.
Why can't the liquid to gas generation keep up with the RCS demand?
I was trying to get my head around how all this would work, in terms of tanking, for all the different engines. You've got the Raptors (pump-fed liquid), the RCS (pressure-fed gas) and now the soft-landers (pressure-fed liquid), all using methane and oxygen, right? All three are presumably in use during moon landings. And you need to keep it all in the correct state and pressure for when it's needed.If they need to regasify the liquid oxygen and liquid methane (stored as liquids for volume and storage tank mass concerns) before burning it in their RCS system, how do they do so? Will they need some sort of heat engine and gas storage bottle buffer to run the smaller thrusters for small maneuvers and corrections without firing up their, presumably fuel burning, heat engine?
- The high pressure LOx and LCH4 tanks are only for the "soft landing" engines, not the RCS thrusters. "soft landing" rockets would use liquid liquid injectors (possibly pintle). RCS thrusters continue to be be gas gas.
John
Would this (oversimplified) diagram be in any way representative?
Sorry John I wasn't clear...
As understand it
Liquid is pumped from the header tanks into a high pressure gas tank and heated if necessary to create high pressure gas source for the RCS.
Repeat as necessary to keep it pressurized.
Why can't this be a continuous process?
Do we need two sets of tanks to alternate between? Use one and fill the other then switch?
- I think so. You would also need lines and electric pumps from the header tanks to the HP gas tanks to recharge them after a sequence of maneuvers. When the Raptors are firing they may be used for HP gas replenishment but you would also need lines and electric pumps from the header tanks to the HP gas tanks to recharge them after a sequence of RCS maneuvers when the Raptors are not running. Also, after a long stay on Mars or the Moon, you will need to recharge your HP gas in order to start the raptors.Thanks John.
Here is a sequence of operation:
Assumptions:
- HP propellant tanks are sized for "soft landing" delta V and are empty.
- HP gas tanks are at pressure (~ 70-100 bar?) and are sized for worse case RCS maneuver sequence or "soft
landing" tank pressurization, what ever is greater.
Preparation for Lunar landing assuming HP liquid tanks are empty:
- liquid propellants flow from the header tanks into the HP "soft landing" tanks.
- HP liquid tanks are sealed off and pressurized by HP gas tanks.
- HP gases maintain HP liquid tank pressure during "soft landing" burn (~30-60 bar ?)
Preparation for launching Blue assumes you are going to use "soft takeoff" rockets:
- Charge HP gas using header tank liquids pumped into HP gas tanks and heated to obtain to the desired pressure
and temperature.
- liquid propellants flow from the header tanks into the HP "soft takeoff" tanks.
- HP liquid tanks are sealed off and pressurized by HP gas tanks.
- HP gases maintain HP liquid tanks pressure during "soft takeoff" burn (~30-60 bar ?)
John
- I think so. You would also need lines and electric pumps from the header tanks to the HP gas tanks to recharge them after a sequence of maneuvers. When the Raptors are firing they may be used for HP gas replenishment but you would also need lines and electric pumps from the header tanks to the HP gas tanks to recharge them after a sequence of RCS maneuvers when the Raptors are not running. Also, after a long stay on Mars or the Moon, you will need to recharge your HP gas in order to start the raptors.Thanks John.
Here is a sequence of operation:
Assumptions:
- HP propellant tanks are sized for "soft landing" delta V and are empty.
- HP gas tanks are at pressure (~ 70-100 bar?) and are sized for worse case RCS maneuver sequence or "soft
landing" tank pressurization, what ever is greater.
Preparation for Lunar landing assuming HP liquid tanks are empty:
- liquid propellants flow from the header tanks into the HP "soft landing" tanks.
- HP liquid tanks are sealed off and pressurized by HP gas tanks.
- HP gases maintain HP liquid tank pressure during "soft landing" burn (~30-60 bar ?)
Preparation for launching Blue assumes you are going to use "soft takeoff" rockets:
- Charge HP gas using header tank liquids pumped into HP gas tanks and heated to obtain to the desired pressure
and temperature.
- liquid propellants flow from the header tanks into the HP "soft takeoff" tanks.
- HP liquid tanks are sealed off and pressurized by HP gas tanks.
- HP gases maintain HP liquid tanks pressure during "soft takeoff" burn (~30-60 bar ?)
John
I presume pumps that can handle those pressures (70-100 bar) are practical for this kind of application? Not too heavy, or requiring too much power?
Updated diagram attached.
Sorry John I wasn't clear...
As understand it
Liquid is pumped from the header tanks into a high pressure gas tank and heated if necessary to create high pressure gas source for the RCS.
Repeat as necessary to keep it pressurized.
Why can't this be a continuous process?
Do we need two sets of tanks to alternate between? Use one and fill the other then switch?
- It could be a continuous process. Too keep up with the needs of the soft landing rockets you need large electric pumps with thousands of hp. Also there is no need to gasify the propellants, that just takes more power.
- If you don't need to keep up, you can spread the pumping over a longer period of them and reduce the pump size and power by an order of magnitude. Its all about optimizing the mass of the system while maintaining needed functionality.
John
Sorry John I wasn't clear...
As understand it
Liquid is pumped from the header tanks into a high pressure gas tank and heated if necessary to create high pressure gas source for the RCS.
Repeat as necessary to keep it pressurized.
Why can't this be a continuous process?
Do we need two sets of tanks to alternate between? Use one and fill the other then switch?
- It could be a continuous process. Too keep up with the needs of the soft landing rockets you need large electric pumps with thousands of hp. Also there is no need to gasify the propellants, that just takes more power.
- If you don't need to keep up, you can spread the pumping over a longer period of them and reduce the pump size and power by an order of magnitude. Its all about optimizing the mass of the system while maintaining needed functionality.
John
Thanks that make sense
You end up with a trade off of two different systems total weight verses complexity.
These landing rockets will only be used on the moon, right?
With the existing two (redundant) pumps rotating between through empty tanks how many tanks would be needed for the lunar landing?
What would be the weight difference of this verses a new liquid engine system?
Great diagram. However I think there will not be any header tanks.- I think so. You would also need lines and electric pumps from the header tanks to the HP gas tanks to recharge them after a sequence of maneuvers. When the Raptors are firing they may be used for HP gas replenishment but you would also need lines and electric pumps from the header tanks to the HP gas tanks to recharge them after a sequence of RCS maneuvers when the Raptors are not running. Also, after a long stay on Mars or the Moon, you will need to recharge your HP gas in order to start the raptors.Thanks John.
Here is a sequence of operation:
Assumptions:
- HP propellant tanks are sized for "soft landing" delta V and are empty.
- HP gas tanks are at pressure (~ 70-100 bar?) and are sized for worse case RCS maneuver sequence or "soft
landing" tank pressurization, what ever is greater.
Preparation for Lunar landing assuming HP liquid tanks are empty:
- liquid propellants flow from the header tanks into the HP "soft landing" tanks.
- HP liquid tanks are sealed off and pressurized by HP gas tanks.
- HP gases maintain HP liquid tank pressure during "soft landing" burn (~30-60 bar ?)
Preparation for launching Blue assumes you are going to use "soft takeoff" rockets:
- Charge HP gas using header tank liquids pumped into HP gas tanks and heated to obtain to the desired pressure
and temperature.
- liquid propellants flow from the header tanks into the HP "soft takeoff" tanks.
- HP liquid tanks are sealed off and pressurized by HP gas tanks.
- HP gases maintain HP liquid tanks pressure during "soft takeoff" burn (~30-60 bar ?)
John
I presume pumps that can handle those pressures (70-100 bar) are practical for this kind of application? Not too heavy, or requiring too much power?
Updated diagram attached.
Great diagram. However I think there will not be any header tanks.- I think so. You would also need lines and electric pumps from the header tanks to the HP gas tanks to recharge them after a sequence of maneuvers. When the Raptors are firing they may be used for HP gas replenishment but you would also need lines and electric pumps from the header tanks to the HP gas tanks to recharge them after a sequence of RCS maneuvers when the Raptors are not running. Also, after a long stay on Mars or the Moon, you will need to recharge your HP gas in order to start the raptors.Thanks John.
Here is a sequence of operation:
Assumptions:
- HP propellant tanks are sized for "soft landing" delta V and are empty.
- HP gas tanks are at pressure (~ 70-100 bar?) and are sized for worse case RCS maneuver sequence or "soft
landing" tank pressurization, what ever is greater.
Preparation for Lunar landing assuming HP liquid tanks are empty:
- liquid propellants flow from the header tanks into the HP "soft landing" tanks.
- HP liquid tanks are sealed off and pressurized by HP gas tanks.
- HP gases maintain HP liquid tank pressure during "soft landing" burn (~30-60 bar ?)
Preparation for launching Blue assumes you are going to use "soft takeoff" rockets:
- Charge HP gas using header tank liquids pumped into HP gas tanks and heated to obtain to the desired pressure
and temperature.
- liquid propellants flow from the header tanks into the HP "soft takeoff" tanks.
- HP liquid tanks are sealed off and pressurized by HP gas tanks.
- HP gases maintain HP liquid tanks pressure during "soft takeoff" burn (~30-60 bar ?)
John
I presume pumps that can handle those pressures (70-100 bar) are practical for this kind of application? Not too heavy, or requiring too much power?
Updated diagram attached.
Header tanks sized for Earth landing contain 30 tonnes of propellant and are required to minimise slosh issues during the flip before landing and to balance the mass distribution during entry.
Header tanks sized for Mars landing contain 66 tonnes of propellant on my figures and are needed for slosh prevention, mass distribution and to provide insulated storage during the trip to Mars.
Header tanks sized for a Moon landing would need to contain several hundred tonnes of landing propellant and a slightly smaller amount for takeoff. They would have total capacity of around one third the total propellant mass and are not needed for mass distribution or slosh prevention with tail first braking and landing. They are called the main tanks at this point and there is no need for additional tankage.
Incidentally the main tanks probably will be externally insulated with MLI before being painted to reduce heat gain during transit to the Moon and loitering waiting for Orion. This will also serve to reduce boiloff of propellant during the surface stay on the Moon.
So Long story short we assume Moonship will have 4 engine types:Before I make a schematic, why wouldn't HPLT with heater/evaporator on the line after it subtitute multiple HPGT?
1. 3x Sea level raptor (SLR) (3)
2. 3x Vacuum Raptor (VR)
3. 9x Yet unnamed Liquid Methalox pressure fed engine for landing (Kestrel on Meth ?) (KM)
4. ?x Gasseous Methane-Oxygen RCS thrusters (RCS)
The propellant system would be symmetric, with each system duplicated for both (liquid/gasseous) Oxygen and (liquid/gasseous) Methane
As such there'd be (at least) 3 tank pairs:
1. High pressure gaseous propellant tank (HPG(x)T) (where x is O or M)
2. High pressure liquid propellant tank (HPL(x)T)
3. Low pressure (main) liquid propellant tank (M(x)T)
Although for redundancy and weight distribution it would probably make sense to have the high pressure tanks in triplets, each feeding and getting fed their own subset of RCS and main engines
HPG(x)Ts have 3 inlets:
1. Gas feeds from Raptor preburners (both SL and Vac) (high volume, high pressure feed needed during raptor operation)
2. Pump feeds from main tank through evaporation heater (low volume, high pressure feed to re-pressure after long coast/sitting on the moon)
3. Valve controlled crossfeed between the 3 systems (redundancy)
HPG(x)Ts have 4 outlets:
1. Pressurization for main tank
2. Pressurization for HPL(x)Ts
3. RCS thrusters
4. Crossfeed between systems
HPL(x)Ts have 2 inlets:
1. Liquid propellant feed from main tank (possibly through propellant tank)
2. Pressurization from HPG(x)Ts
HPL(x)Ts have 2 outlets:
1. Kestrel on Meth (KM) landing engines
2. Drain to main tank
M(x)Ts have 3 inlets:
1. Drain from HPL(x)Ts
2. Propellant transfer system feed (might double as GST for pad fueling)
3. Pressurization from HPG(x)Ts
M(x)Ts have 4 outlets:
1. Propellant transfer system drain (might double for circularisation for pad GST)
2. Pumped feed to HPL(x)Ts
3. Supply for Sea level and Vacuum Raptors
4. outboard vent (to get rid of surplus ulage pressure due to boiloff)
Ideally you'd have a temperature control system of some sorts, for long missions, using a separate coolant loop, radiators and heat pumps.
Purpose:
1. Cool down main M(x)T to prevent boiloff
2. Heat HPG(x)T (prevent condensation)
3. Evaporate propellant to replenish HPG(x)T
4. Temperature control of mechanical and electronic components to prevent heat/cold soak (valves, computers, batteries, engines, etc...)
Would that work?
Does anyone want to make a diagram?
Edit: Shouldn't forget, both Rapor and Kestrel on Meth would need high pressure gas feeds for ignitors
Raptors might also need high pressure gas for startup/spoolup (unless they use helium)
At a rough estimate, the landing engines might need to hover for 20 seconds in one lunar gravity, Maybe less if they know exactly where they're going to touchdown and just turn on briefly to cushion the fall. Maybe more if they need time to find the best spot, or correct for main engine descent positional errors. (They won't have GPS on the Moon, at least initially.) Also more if they want to take off using the landing engines, but the tanks can be topped up again from the main tanks for that.Don't be over complicating the landing thruster design - it just needs to soften the impact to a survivable litho break, and advanced rocket engines take longer to develop. The schedules long, the part is wrong.
So assume 30 m/s delta v:
For a (maximal) 120 t dry SS, with 150 t cargo and 180 t return propellant, that's 450 t landing mass.
At 320 Isp, that's about 4.4 t of liquid landing propellant. At an average density of 0.8 that's about 5.5 m3 tank volume.
For pressure fed engines, that's a lot of high pressure gas needed to keep the pressure up around 30 to 40 bar, until the tanks are almost empty.
Whereas, if say expander cycle engines were used, the landing tanks might only need to be pressurized to 3 or 4 bar. Besides using a little less propellant due to higher Isp.
The engines could even be fed directly from the main tanks, which would be still pressurized from the Raptor autogenous feed.
Or just tap the main tank pressurant gasses. The pressure in the huge main tanks would barely drop for that amount, either way.
Don't be over complicating the landing thruster design - it just needs to soften the impact to a survivable litho break, and advanced rocket engines take longer to develop. The schedules long, the part is wrong.
At a rough estimate, the landing engines might need to hover for 20 seconds in one lunar gravity, Maybe less if they know exactly where they're going to touchdown and just turn on briefly to cushion the fall. Maybe more if they need time to find the best spot, or correct for main engine descent positional errors. (They won't have GPS on the Moon, at least initially.) Also more if they want to take off using the landing engines, but the tanks can be topped up again from the main tanks for that.
So assume 30 m/s delta v:
For a (maximal) 120 t dry SS, with 150 t cargo and 180 t return propellant, that's 450 t landing mass.
At 320 Isp, that's about 4.4 t of liquid landing propellant. At an average density of 0.8 that's about 5.5 m3 tank volume.
For pressure fed engines, that's a lot of high pressure gas needed to keep the pressure up around 30 to 40 bar, until the tanks are almost empty.
Whereas, if say expander cycle engines were used, the landing tanks might only need to be pressurized to 3 or 4 bar. Besides using a little less propellant due to higher Isp.
The engines could even be fed directly from the main tanks, which would be still pressurized from the Raptor autogenous feed.
Or just tap the main tank pressurant gasses. The pressure in the huge main tanks would barely drop for that amount, either way.
Don't be over complicating the landing thruster design - it just needs to soften the impact to a survivable litho break, and advanced rocket engines take longer to develop. The schedules long, the part is wrong.
The schedule would only be long IF they were starting from scratch recently. We have no real idea what they might have been playing with on that scale over the last few years. Plus there are a few existing, working, LOX\LCH4 engines, at that size, out there that they could buy or licence.
100 kN is near the sweet spot for expanders. The turbines run at around room temperature, on cryo fuel vaporized by regen cooling of the chamber and nozzle. Not a harsh regime.
It could be argued that the extra high pressure tanks, lines, and recharging requirements of pressure fed engines are the real unnecessary complications. Compared to low-temp turbo-pumps on engines, that probably already have regen cooling, and low pressure propellant lines from existing tanks.
At a rough estimate, the landing engines might need to hover for 20 seconds in one lunar gravity...
...if say expander cycle engines were used, the landing tanks might only need to be pressurized to 3 or 4 bar.
100 kN is near the sweet spot for expanders. The turbines run at around room temperature, on cryo fuel vaporized by regen cooling of the chamber and nozzle.
At a rough estimate, the landing engines might need to hover for 20 seconds in one lunar gravity...
...if say expander cycle engines were used, the landing tanks might only need to be pressurized to 3 or 4 bar.100 kN is near the sweet spot for expanders. The turbines run at around room temperature, on cryo fuel vaporized by regen cooling of the chamber and nozzle.
That's a fuel-only, not a dual, expander cycle?
What's the envisioned heat exchanger function at the start of soft-landing descent?
At a rough estimate, the landing engines might need to hover for 20 seconds in one lunar gravity...
...if say expander cycle engines were used, the landing tanks might only need to be pressurized to 3 or 4 bar.100 kN is near the sweet spot for expanders. The turbines run at around room temperature, on cryo fuel vaporized by regen cooling of the chamber and nozzle.
That's a fuel-only, not a dual, expander cycle?
What's the envisioned heat exchanger function at the start of soft-landing descent?
Fuel only probably. As pointed out, complexity should be kept to a minimum and ultra-efficiency is not needed for these engines.
Typically expanders use ambient temperature of the metal chamber and nozzle for the initial heating of the cryo fluid, then gradually spool up, over a second or two, to full working temperature.
This link (https://space.stackexchange.com/questions/39536/how-do-expander-cycle-engines-inject-liquid-fuel-during-startup) explains how the RL-10 handles it. Note: an RL-10 has been experimentally run on CH4.
If between uses the landing engines are in a spot that gets too cold, there are simple mitigation options. e.g. Running electrical heaters or torch igniters to pre-warm the engines, before use.
There's no doubt these engines would be more complex than pressure fed, but eliminating high pressure liquid cryo tanks, nine sets of high pressure feed lines, and all the rest, may well be worth it. If something breaks, you've probably just lost one of nine landing engines, not the whole system.
At a rough estimate, the landing engines might need to hover for 20 seconds in one lunar gravity...
...if say expander cycle engines were used, the landing tanks might only need to be pressurized to 3 or 4 bar.100 kN is near the sweet spot for expanders. The turbines run at around room temperature, on cryo fuel vaporized by regen cooling of the chamber and nozzle.
That's a fuel-only, not a dual, expander cycle?
What's the envisioned heat exchanger function at the start of soft-landing descent?
Fuel only probably. As pointed out, complexity should be kept to a minimum and ultra-efficiency is not needed for these engines.
Typically expanders use ambient temperature of the metal chamber and nozzle for the initial heating of the cryo fluid, then gradually spool up, over a second or two, to full working temperature.
This link (https://space.stackexchange.com/questions/39536/how-do-expander-cycle-engines-inject-liquid-fuel-during-startup) explains how the RL-10 handles it. Note: an RL-10 has been experimentally run on CH4.
If between uses the landing engines are in a spot that gets too cold, there are simple mitigation options. e.g. Running electrical heaters or torch igniters to pre-warm the engines, before use.
There's no doubt these engines would be more complex than pressure fed, but eliminating high pressure liquid cryo tanks, nine sets of high pressure feed lines, and all the rest, may well be worth it. If something breaks, you've probably just lost one of nine landing engines, not the whole system.
You just voiced a very important reason why an expander cycle engine would probably be a bad idea for the landing. It's spool-up is way too slow. For final approach and touchdown you need an engine that can be deep throttled, is high thrust and react to throttle changes ultra fast - both up and down.
An expander cycle engine can be deep throttled, but its neither high thrust nor does it react fast, especially when its cold. (It can also have quite horrible transients when thrust is reduced due to the expanding residual propellant in the cooling channels.)
^^^ But it's all one system though. 70 bar HP tanks to power the maneuvering RCS and also press the main tanks. Those 70 bar tanks can be much larger to power the landing engines. Or be much smaller if the landing engines run off the main tanks at 6 bar. If we're discussing tradeoffs, one thread is good for that.70 bar tanks for pressurizing the main tanks would be large and heavy. Simple CH4 burner would pressure the main tanks much easier if needed.
From where do we know that there will be pressure fed moon landing engines? Why not small open cycle or electric pump fed? Best tank is no tank.
The tesla motor operates a hydraulic pump. Hydraulic fluid. So if you want to put it in a RCS system you’ll have to explain how...From where do we know that there will be pressure fed moon landing engines? Why not small open cycle or electric pump fed? Best tank is no tank.
We don't. Hence all the speculation, and how it affects the presumably pressure fed RCS system.
Recent speculation on (I think) the prototypes thread, was that the pump powered by a Tesla motor might be for providing high pressure gas for RCS, without needing large storage tanks, just small accumulators.
This wouldn't be nearly large enough for landing engines, and if they were doing electric pumping, liquid would be more logical than gas, given the landing propellant volumes.
IMHO, if the pump and motor are for pressurizing gas, it's to refill large COPV tanks for RCS and other uses. I expect the landing engines to use a fairly basic, expander or electric pump cycle.
From where do we know that there will be pressure fed moon landing engines? Why not small open cycle or electric pump fed? Best tank is no tank.
We don't. Hence all the speculation, and how it affects the presumably pressure fed RCS system.
Recent speculation on (I think) the prototypes thread, was that the pump powered by a Tesla motor might be for providing high pressure gas for RCS, without needing large storage tanks, just small accumulators.
This wouldn't be nearly large enough for landing engines, and if they were doing electric pumping, liquid would be more logical than gas, given the landing propellant volumes.
IMHO, if the pump and motor are for pressurizing gas, it's to refill large COPV tanks for RCS and other uses. I expect the landing engines to use a fairly basic, expander or electric pump cycle.
From where do we know that there will be pressure fed moon landing engines? Why not small open cycle or electric pump fed? Best tank is no tank.
We don't. Hence all the speculation, and how it affects the presumably pressure fed RCS system.
Recent speculation on (I think) the prototypes thread, was that the pump powered by a Tesla motor might be for providing high pressure gas for RCS, without needing large storage tanks, just small accumulators.
This wouldn't be nearly large enough for landing engines, and if they were doing electric pumping, liquid would be more logical than gas, given the landing propellant volumes.
IMHO, if the pump and motor are for pressurizing gas, it's to refill large COPV tanks for RCS and other uses. I expect the landing engines to use a fairly basic, expander or electric pump cycle.
The existing RCS has two edge cases:
in space operations small, precise thrust
cross wind landing large, precise thrust
the tanks are sized for landing operations using small efficient liquid pumps.
With the new lunar landing (and take off):
why not use the existing EDL RCS system
the tanks are sized for space operations using small efficient liquid pumps
landing operations use larger efficient liquid pumps feeding the common tank system.
From where do we know that there will be pressure fed moon landing engines? Why not small open cycle or electric pump fed? Best tank is no tank.
We don't. Hence all the speculation, and how it affects the presumably pressure fed RCS system.
Recent speculation on (I think) the prototypes thread, was that the pump powered by a Tesla motor might be for providing high pressure gas for RCS, without needing large storage tanks, just small accumulators.
This wouldn't be nearly large enough for landing engines, and if they were doing electric pumping, liquid would be more logical than gas, given the landing propellant volumes.
IMHO, if the pump and motor are for pressurizing gas, it's to refill large COPV tanks for RCS and other uses. I expect the landing engines to use a fairly basic, expander or electric pump cycle.
The existing RCS has two edge cases:
in space operations small, precise thrust
cross wind landing large, precise thrust
the tanks are sized for landing operations using small efficient liquid pumps.
With the new lunar landing (and take off):
why not use the existing EDL RCS system
the tanks are sized for space operations using small efficient liquid pumps
landing operations use larger efficient liquid pumps feeding the common tank system.
- There is no indication that the RCS uses liquid rockets. Indications are the are gaseous fed.
- RCS rockets could be sized for EDL, we don't know, but there is no indication that they are liquid or pump fed. Indications are that they are gaseous, pressure fed.
John
The planned RCS thruster is optimized for sea level operation.Huh? Why would you optimise RCS for sea level?
What would a vacuum optimized version look like?
I will note that one RCS pod on Hopper has been removed (each RCS location around Hopper was comprised of two RCS pods from F9 and only the left / right thrusters were plumbed for each pod).
Huh? Why would you optimise RCS for sea level?
Seriously confusd ???
Ah, yes. That makes sense.Huh? Why would you optimise RCS for sea level?A vacuum-optimized nozzle can lead to flow separation when fired in a dense atmosphere, which can damage the nozzle, and I suspect it can also lead to unpredictable thrust vectors. So if you want to fire the RCS thrusters at sea-level, they must not be vacuum-optimized. Firing an engine optimized for sea-level in vacuum, on the other hand, only wastes some performance.
Seriously confusd ???
Huh - yup!I will note that one RCS pod on Hopper has been removed (each RCS location around Hopper was comprised of two RCS pods from F9 and only the left / right thrusters were plumbed for each pod).
If you're making that observation from seeing that Hopper itself is missing one, you should know that Musk presented Yusaku Maezawa one of the RCS pods as a gift.
https://mobile.twitter.com/thesheetztweetz/status/1196774568200941568
Ah, yes. That makes sense.Huh? Why would you optimise RCS for sea level?A vacuum-optimized nozzle can lead to flow separation when fired in a dense atmosphere, which can damage the nozzle, and I suspect it can also lead to unpredictable thrust vectors. So if you want to fire the RCS thrusters at sea-level, they must not be vacuum-optimized. Firing an engine optimized for sea-level in vacuum, on the other hand, only wastes some performance.
Seriously confusd ???
Thanks.
Question regarding the RCS thrusters: Raptor already uses ignition torches in the preburners, which are like small combustion chambers themselves. Could a methalox thruster be based on a repurposed Raptor preburner?
I'm NO expert, but the preburners are physically extremely integrated into the raptor engine. Not something that could be taken out. ALso AIUI each depends on the environment the other creates. Also each burns a massively ASYMMETRIC mixture, so the overwhelming majority of the gaseous output of each is either unused oxygen, or unburnt methane. So they are totally unsuited to work individually as rocket engines. Then their mass flow is jointly approaching one tonne (1/2?) per second.... which is totally inappropriate for a thruster!Question regarding the RCS thrusters: Raptor already uses ignition torches in the preburners, which are like small combustion chambers themselves. Could a methalox thruster be based on a repurposed Raptor preburner?
This sounds akin to taking the starter motor out of a truck, attaching it to your bike and calling it an electric scooter. It might be physically possible, but it's hard to imagine that it would be the best option by any metric.
[...] here’s a lightly edited version of what was said [at 35 minutes of the video by Nicholas Cummings of SpaceX]:QuoteFor the terminal descent of Starship, a few tens of meters before we touchdown on the lunar surface, We actually use a high thrust RCS system so we don’t impinge on the surface of the moon with a high thrust Raptor engine. The thrusters planned have a lot of heritage in the Raptor design itself. It uses the same methane and oxygen propellants as Raptor, so there’s a lot of commonality there. Going to be ramping up some very rapid testing activities in the coming year.
Question by Tim Todd: Raptors will only do majority of the work flipping on the first couple flights right? Won't the hot gas thrusters do more of the work eventually?
Answer by Elon Musk: It’s counter-intuitive, but Raptor has so much thrust at high Isp with liquid (high density) propellant & pump-fed (light tanks), that it beats hot gas for the flip. That said, hot gas beats the heck out of N2 for orbital manuevers & stabilizing ship if landing in high winds!
Axis | Linear acceleration [ft/s2] |
+X | 0.21 |
-X | 0.22 |
±Y | 0.16 |
+Z | 0.32* |
-Z | 0.42 |
Axis | Angular acceleration [deg/s2] |
±Roll | 0.92 |
+Pitch | 1.23 |
-Pitch | 0.85 |
±Yaw | 0.70 |
Some recent discussion on the topic of "use the same 100 kN thruster for RCS and Moon landing" had me doing a bit of a comparison with the Shuttle so I decided to dust of this rather more on-topic thread hoping against all reason that some relevant discussion might find its way here ;)
The Shuttle crew operations manual (PDF) (http://390651main_shuttle_crew_operations_manual.pdf) has some nice tables of average orbiter RCS acceleration on page 9.2-3 (p. 1009 in the PDF). For a heavy payload (260 klbs) in normal orbital mode these are:*There is also a HIGH mode that can fire all thrusters to back away from a payload at 0.94 ft/s2.
Axis Linear acceleration [ft/s2] +X 0.21 -X 0.22 ±Y 0.16 +Z 0.32* -Z 0.42
Axis Angular acceleration [deg/s2] ±Roll 0.92 +Pitch 1.23 -Pitch 0.85 ±Yaw 0.70
From these numbers it looks like 0.2 ft/s2 (~6cm/s2) and 1 deg/s2 are reasonable for general maneuvering. Using a quick and dirty model for a fully fueled Starship at 1450 t with payload consisting of four stacked solid solid cylinders (Skirt: 5 m, 27 t. Oxygen: 12 m, 939t. Methane: 9 m, 261 t. Nose: 23 m, 223 t) i get a center of mass at 16.8 m (right at the methane header tank) and a moment of inertia for pitch/yaw of ~1.3e8 kgm2 with roll about 1/10 of that. Placing RCS thrusters at the "corners" (front end of forward flaps and aft end of the skirt) gives a average moment arm of ~22 m for pitch/yaw and 4.5 m for roll, so pitch/yaw is the limiting case.
1450 t * 6 cm/s2 = 90 kN
1.3e8 kgm2 * 1 deg/s2 / 22 m = 2 x 53 kN
So you can make an argument for 100 kN RCS thrusters if you want a fully loaded Starship to be able to make higher acceleration maneuvers like the back-off mentioned above (which would need four of them). For general Shuttle like maneuverability something like 25 kN thrusters in a decently redundant configuration should be enough and that is only if you insist on moving the full Starship massing 3 x the ISS. For docking for example you would rather be docking things to it - in most Starship dockings at least one of them will be <300 t for which something like 5-10 kN is more reasonable (which should still be plenty for a 1450 t Starship to hold position and control attitude).
I still think they should maximize on their strengths, and ISP, by going the Electron - Rutherford way.
They will already have most the battery capacity onboard, and can regenerate using solar.
Anyone else's thoughts on going with Electric Pumped Fed Hot Gas Design for the Starship RCS/Landing Thrusters?
This. Electric pumps can be for Methalox, or for charging Methox tanks. I would imagine electric pump-charged Methox is better because you don't need giant banks of batteries.
I still think they should maximize on their strengths, and ISP, by going the Electron - Rutherford way.
They will already have most the battery capacity onboard, and can regenerate using solar.
Anyone else's thoughts on going with Electric Pumped Fed Hot Gas Design for the Starship RCS/Landing Thrusters?
Can you clarify what you mean by a "Electric Pumped Fed Hot Gas"?
The way I understand it, an electric pump system, like in the Rutherford engine, moves liquids. A hot gas system is inherently pressure fed because the fuel and oxidized are already under high pressure.
Pump power is inversely proportional to fluid density. You don't want to pump low density gases.Unless you have a large gaseous RCS reservoir that you can continuously top up slowly when not in use. Or else just pump some methalox and then vaporize it with resistive heaters. Either or. Pumping boiloff into the RCS tanks would help with cooling though.
John
Interesting. The patterns seem unlikely to be possible from a Raptor. But how do you rule out testing of a Super Draco?Aren't Super Dracos only meant to fire for constant duration to pull Crew Dragon off a booster? And they seem like they would be so loud. I mean look at this.
Interesting. The patterns seem unlikely to be possible from a Raptor. But how do you rule out testing of a Super Draco?Aren't Super Dracos only meant to fire for constant duration to pull Crew Dragon off a booster? And they seem like they would be so loud. I mean look at this.
https://www.youtube.com/watch?v=lIGVi_rMFGw
Either they've got a solitary Raptor preburner that's a complete jalopy running with cold spark plugs and has a backfiring problem, or that's Starship methox RCS.
That's why I say seem. Not very objective, but the pulsing is another story.Interesting. The patterns seem unlikely to be possible from a Raptor. But how do you rule out testing of a Super Draco?Aren't Super Dracos only meant to fire for constant duration to pull Crew Dragon off a booster? And they seem like they would be so loud. I mean look at this.
https://www.youtube.com/watch?v=lIGVi_rMFGw
Either they've got a solitary Raptor preburner that's a complete jalopy running with cold spark plugs and has a backfiring problem, or that's Starship methox RCS.
Comparing a video/audio taken feet away from the engine compared to video/audio at a substantial distance isn't great for comparing loudness, I suspect.
Yea, I don't recall footage of a SuperDraco pulsing like the mystery audio contains, but it doesn't mean someone else hasn't seen it. I am just trying to approach from the point of view that if we can't prove it is a new hot-gas thruster for Starship, lets try to exclude existing components like Draco, SuperDraco.
I hope they do a hop test with a belt of 24 of those thrusters. That would be a sight!
There is a problem with your rule of thumb. Starship holds 1200 tons of fuel. Although you probably wouldn't have a circumstance where it would be full while you land on the Moon, even if you just wanted the ability to land with a 1/4 of a tank that would mean the thruster belt would have to put out ((80t(LSS) + 80t(payload) +300t fuel) * 1.5 (thrust to weight)) at 1/6 the Earth's gravity.It was just a rule of thumb. Still works though because Starship's dry mass is more than 100 tons. Why do a hop though? Flying in a vacuum is relatively simple. And none of the engines have thrust vectoring to worry about. They'll also likely be pressure fed. I mean, the only real concerns are reliably getting the engines to fire in a vacuum and vibrational issues.
101 tons.
There is a problem with your rule of thumb. Starship holds 1200 tons of fuel. Although you probably wouldn't have a circumstance where it would be full while you land on the Moon, even if you just wanted the ability to land with a 1/4 of a tank that would mean the thruster belt would have to put out ((80t(LSS) + 80t(payload) +300t fuel) * 1.5 (thrust to weight)) at 1/6 the Earth's gravity.
101 tons.
The delta-v from NHRO to land on the moon is at least 2.5 km/s... So Lunar Starship will need to be able to land with enough propellant to make it back to NHRO and Gateway/Orion. How much propellant is that? I'll leave that to others. :) But I suspect it is in the 1/3 to 1/4 full range.
6.9 km/s with 100 tons of cargo. You can go way further if you pack fewer granola bars. Also, I've been looking for a delta-v map that includes NRHO forever! Thank you so much for posting that. But WHAT on God's green Earth is that visual communication. Holy cow. It's like the attractiveness and succinctness of a dV map is inversely proportional to how interesting the information is that it conveys.The delta-v from NHRO to land on the moon is at least 2.5 km/s... So Lunar Starship will need to be able to land with enough propellant to make it back to NHRO and Gateway/Orion. How much propellant is that? I'll leave that to others. :) But I suspect it is in the 1/3 to 1/4 full range.
This shows 2.75 km/s for each trip = 5.5km/s down & back, PLUS 3.65 km/s for LSS to get there from LEO.
Total Dv budget of 9.15 km/s.
Didn't Elon quote 6.9 km/s as SS' number?
Which suggests LSS can't meet Orion in NRHO & take crew to/from the moon.
Where else can Orion, with a 1.2 km/s capability meet LSS & get back to Earth plus LSS can take crew to the moon & back?
HEO?
Why do a hop though? Flying in a vacuum is relatively simple. And none of the engines have thrust vectoring to worry about. They'll also likely be pressure fed. I mean, the only real concerns are reliably getting the engines to fire in a vacuum and vibrational issues.
Gravity is a body force and so pulls on all parts of Starship the same. So long as it hasn't hit the ground yet or been subjected to black hole tidal forces or something, gravity is not a force that can dynamically affect the vehicle. Even including gravity, the free body diagram for SS on these waist thrusters is dead simple. There is a single mass and a single moment of Inertia that is centered at some point below the thruster belt on the centerline of the vehicle, and then you have 24 vectors of thrust force that can be pulsed on and off which point at some angle between straight out and straight down positioned radially about the vehicle. The only other force is gravity. It's constant and does not exert any moments so it plays very nice with the math.Why do a hop though? Flying in a vacuum is relatively simple. And none of the engines have thrust vectoring to worry about. They'll also likely be pressure fed. I mean, the only real concerns are reliably getting the engines to fire in a vacuum and vibrational issues.
Why do a hop? Well, it's true it might not be needed.
On the other hand, you are dealing with an object in gravity, landing, and taking off. It is being supported by thrust from a rather unusual location rather high up but not above the craft with a center of gravity that would vary widely depending on payload and fuel. You have a system that contains... what?... 24 engines. They are potentially, individually controlled, to adapt to any failures. There could actually be vectoring of thrust by changing the power by different quadrants. They might want to verify their models...
They might want to test it.
Also, I've been looking for a delta-v map that includes NRHO forever!
Okay I'm desparate to share this with you or anyone who will listen. You know how I said the visual communication was atrocious? Look how much better this is. And I did it in MS Paint. You can immediately go from one place to another and it's much more obvious what is going on. I did exclude pure TLI delta-v but included it in figures for going to different Lunar orbits from Earth. And it's crusty as all get out. But still!Also, I've been looking for a delta-v map that includes NRHO forever!
Not a map, but there is a table in the Wikipedia page for Delta-v budget (https://en.wikipedia.org/wiki/Delta-v_budget#Earth_Lunar_Gateway%E2%80%94high_thrust).
Okay I'm desparate to share this with you or anyone who will listen. You know how I said the visual communication was atrocious? Look how much better this is. And I did it in MS Paint. You can immediately go from one place to another and it's much more obvious what is going on. I did exclude pure TLI delta-v but included it in figures for going to different Lunar orbits from Earth. And it's crusty as all get out. But still!Also, I've been looking for a delta-v map that includes NRHO forever!
Not a map, but there is a table in the Wikipedia page for Delta-v budget (https://en.wikipedia.org/wiki/Delta-v_budget#Earth_Lunar_Gateway%E2%80%94high_thrust).
I may not be afraid of complaining all over the place and armchair redesigning with MS Paint but contributing to the community is a whole other story. Then again, It would be really cool to see a unitary map combining all the big guns into one image. You could have the big Earth-Moon-Mars trio as the focus, with all the funky halo orbits and cycler orbits and lagrange points included. The rest of the solar system could be off to the bottom. That's a project!Okay I'm desparate to share this with you or anyone who will listen. You know how I said the visual communication was atrocious? Look how much better this is. And I did it in MS Paint. You can immediately go from one place to another and it's much more obvious what is going on. I did exclude pure TLI delta-v but included it in figures for going to different Lunar orbits from Earth. And it's crusty as all get out. But still!Also, I've been looking for a delta-v map that includes NRHO forever!
Not a map, but there is a table in the Wikipedia page for Delta-v budget (https://en.wikipedia.org/wiki/Delta-v_budget#Earth_Lunar_Gateway%E2%80%94high_thrust).
Wikipedia is a collaboratory effort. Sign in, clean up a bit your graph, upload it and link it to the article.
Add this one as wellHey, you saved my doodle! I feel so honored, I'm sorry for how crusty it is. I regret that one. Wish it was NRHO instead of LLO but
Add this one as wellHey, you saved my doodle! I feel so honored, I'm sorry for how crusty it is. I regret that one. Wish it was NRHO instead of LLO but
(1) I didn't yet have the NRHO delta-v map that just got posted so I didn't know what the requirements were at the time and
(2) I didn't realize that Orion/EUS/ESM didn't have the delta-v to make LLO and come back. Which is sad, by the way.
Orion docks with LSS in HEO.
Transfers crew, LSS does direct entry, lands moon & returns direct to HEO, no LLO.
Crew transfer to Orion, which lands Earth.
LSS is refuelled for next transfer.
Of course SpaceX could use their Crew Dragon to do this as well.
Which gives SpaceX the ability to send private crew to the moon.
[...] I did it in MS Paint. [...] But still!
I hope they do a hop test with a belt of 24 of those thrusters. That would be a sight!
The nice thing about that is you can rule of thumb it just by the ratio between Moon and Earth gravity. If a 120 ton Starship laden with 100 tons of cargo can land on the Moon then it should be able to do the same on Earth if the vehicle/cargo total mass was...
37 tons.
Dry mass of SS is 120 tons. Even if the TWR during a Moon landing is as high as 2 that means a hop can't be performed at all unless the test vehicle and fuel are significantly lighter than 70 tons. Sorry, if they're going to hop on those thrusters it's not going to be in a full scale vehicle. Unless maybe they fire a Raptor or two to simulate Lunar G a la the infamous Flying Beadstead? That would be a challenge because even though Raptors can gimbal a ton by rocket standards they don't have anything on that crazy swivel jet engine.
Good delta-v maps will also include maximum plane change delta-v alongside the primary indicator for transfer dV required. In the diagram the only orbit change that absolutely needs such a plane change is a complete 90 degree shift from a polar LLO to an equatorial LLO. Granted the details of how to efficiently insert from NRHO to an efficient trans-Earth return trajectory currently escape me, but still.[...] I did it in MS Paint. [...] But still!
It's good!
One place it might be improved is somehow showing that the NRHO and LLO trajectories don't (usually) intersect. In particular the low lunar orbits used for Apollo missions were essentially equatorial rather than polar. The astrogation to get from an NHRO to one of those isn't totally straight-forward, to say the least.
That would give a 120 ton dry mass Starship with 100 tons of cargo a Lunar TWR with over 4 assuming no return fuel and a TWR of more than 3 with 100 tons of placeholder methalox also aboard. Not bad! I retract what I said earlier if that's true.I hope they do a hop test with a belt of 24 of those thrusters. That would be a sight!
The nice thing about that is you can rule of thumb it just by the ratio between Moon and Earth gravity. If a 120 ton Starship laden with 100 tons of cargo can land on the Moon then it should be able to do the same on Earth if the vehicle/cargo total mass was...
37 tons.
Dry mass of SS is 120 tons. Even if the TWR during a Moon landing is as high as 2 that means a hop can't be performed at all unless the test vehicle and fuel are significantly lighter than 70 tons. Sorry, if they're going to hop on those thrusters it's not going to be in a full scale vehicle. Unless maybe they fire a Raptor or two to simulate Lunar G a la the infamous Flying Beadstead? That would be a challenge because even though Raptors can gimbal a ton by rocket standards they don't have anything on that crazy swivel jet engine.
John did a calculation of the thrust needed for lunar landing here (https://forum.nasaspaceflight.com/index.php?topic=49622.msg2169758#msg2169758), it needs ~163 ton force, so should be able to hop on Earth.
LEO direct to LLO is only about 4000 m/s, if you don't go via NRHO.Okay, this is why I have reservations about actually attempting to construct my own delta-v map. Using premade values can lead you astray because there may be information that wasn't included but is otherwise important, and calculating figures yourself can also give wrong values because you didn't come up with the most efficient route. Take that figure I gave for going from NRHO to an equatorial LLO. I said the plane change delta-V was twice LLO orbital velocity (an impulsive plane change would kill all polar velocity and add it back in at 90 degrees to the original direction) but I know that's not most efficient because performing the plane change before you circularize the NRHO would allow you to do it at lower total velocity and thus it would be cheaper. My grasp on orbital mechanics is really weak so I think I'd like to leave it alone altogether.
LEO direct to LLO is only about 4000 m/s, if you don't go via NRHO.Okay, this is why I have reservations about actually attempting to construct my own delta-v map. ...
...
Didn't Elon quote 6.9 km/s as SS' number?
Which suggests LSS can't meet Orion in NRHO & take crew to/from the moon.
...
Good delta-v maps will also include maximum plane change delta-v alongside the primary indicator for transfer dV required. In the diagram the only orbit change that absolutely needs such a plane change is a complete 90 degree shift from a polar LLO to an equatorial LLO. Granted the details of how to efficiently insert from NRHO to an efficient trans-Earth return trajectory currently escape me, but still.
Rendezvous Strategies in the Vicinity of Earth-Moon Lagrangian Points
Stephanie Lizy-Destrez1*, Laurent Beauregard1, Emmanuel Blazquez1, Antonino Campolo1,2, Sara Manglativi1,2 and Victor Quet1
1ISAE-SUPAERO, Toulouse, France
2Dipartimento di Scienze e Tecnologie Aerospaziali (DAER), Politecnico di Milano, Milan, Italy
In the context of Human Spaceflight exploration mission scenario, with the Lunar Orbital Platform- Gateway (LOP-G) orbiting about Earth-Moon Lagrangian Point (EML), Rendezvous and Docking (RVD) operational activities are mandatory and critical for the deployment and utilization of the LOP-G (station assembly, crew rotations, cargo delivery, lunar sample return). There is extensive experience with RVD in the two-body problem: in Low Earth Orbit (LEO) to various space stations, or around quasi-circular Low Lunar Orbits (LLO), the latter by Apollo by means of manual RVD. However, the RVD problem in non-Keplerian environments has rarely been addressed and no RVD has been performed to this date in the vicinity of Lagrangian points (LP) where Keplerian dynamics are no longer applicable. Dynamics in such regions are more complex, but multi-body dynamics also come with strong advantages that need to be further researched by the work proposed here. The aim of this paper is to present methods and results of investigations conducted to first set up strategies for far and close rendezvous between a target (the LOP-G, for example) and a chaser (cargo, crew vehicle, ascent and descent vehicle, station modules, etc.) depending on target and chaser orbit. Semi-analytical tools have been developed to compute and model families of orbits about the Lagrangian points in the Circular Restricted Three Body Problem (CR3BP) like NRHO, DRO, Lyapunov, Halo and Lissajous orbits. As far as close rendezvous is concerned, implementation of different linear and non-linear models used to describe cis-lunar relative motion will be discussed and compared, in particular for NRHO and DRO.
Due to shear size of SS and its mass. Hot gas thrusters could made sense. Especially for tight manoeuvring during landing. Maybe is even enabler for possible precise tover landings.You mean pumping cryogenic liquids then burning gas, all without a preburner?
So yeah its application could provide precise grunt for SS and even more importantly for SH. So i m wondering ways how could SpaceX raise efficacy so far crude devices.
Would electric turbopump made sense? I think it could.
1. Made central redundant parallel HIGH pressure electric turbo pump assembly
2. Raise chamber and nozzle pressure on demand pretty much anywhere on ship
3. Avoid preburners and use batteries instead. At slight mass cost but for much easier fire and refire in split second
4. Reduce COPVS complications and its heat losses at minimum. And due its high pressures avoid higher RUD probability because of it.
I would argue that way you could made design of HRCS much more simpler. Especially when you are transferring problem to already known variables - battery, electric engines and electric valves, engine mappings. Plus hey you could pull some Tesla guys for advice in spare time or two. All that areas could be quite easily redundant and controllable in case of any anomaly's. Plus response would be second to none.
An electric cycle engine uses electric pumps to pressurize the propellants from a low-pressure fuel tank to high-pressure combustion chamber levels, generally from 0.2 to 0.3 MPa (29 to 44 psi) to 10 to 20 MPa (1,500 to 2,900 psi). The pumps are powered by an electric motor, with electricity from a battery bank. Source Wiki
Due to shear size of SS and its mass. Hot gas thrusters could made sense. Especially for tight manoeuvring during landing. Maybe is even enabler for possible precise tover landings.While electric turbopumped engines are cool and all, this is just adding unneeded complexity in my opinion. Just use pressure fed COPVs (gox and methane) from the autogenous pressurization system and feed the gas lines from the COPVs to small combustion chambers with a spark plug type igniter. Am I way off track to think that this is a simple and viable solution and probably the path they're taking?
So yeah its application could provide precise grunt for SS and even more importantly for SH. So i m wondering ways how could SpaceX raise efficacy so far crude devices.
Would electric turbopump made sense? I think it could.
1. Made central redundant parallel HIGH pressure electric turbo pump assembly
2. Raise chamber and nozzle pressure on demand pretty much anywhere on ship
3. Avoid preburners and use batteries instead. At slight mass cost but for much easier fire and refire in split second
4. Reduce COPVS complications and its heat losses at minimum. And due its high pressures avoid higher RUD probability because of it.
I would argue that way you could made design of HRCS much more simpler. Especially when you are transferring problem to already known variables - battery, electric engines and electric valves, engine mappings. Plus hey you could pull some Tesla guys for advice in spare time or two. All that areas could be quite easily redundant and controllable in case of any anomaly's. Plus response would be second to none.
Autogenous pressurization system requires running Raptors to maintain pressure.
Autogenous pressurization system requires running Raptors to maintain pressure.Of course, I know that. The COPVs would be pressurized when Raptors are running and store the pressurized gases for later use.
Intriguing audio of the (meth/lox?) thrusters being tested at McGregor, recorded by Nicotine Jenkins on youTube.
Although it's mostly just audio, you can get a sense that some serious progress is being made.
SpaceX McGregor Engine/Thruster Test 04/13/2021 ANGLE #1
https://www.youtube.com/watch?v=vrGS2UtSP5k (https://www.youtube.com/watch?v=vrGS2UtSP5k)
SpaceX McGregor Engine/Thruster Test 04/13/2021 ANGLE #2
https://www.youtube.com/watch?v=DmSsfWK5UIg (https://www.youtube.com/watch?v=DmSsfWK5UIg)
SpaceX McGregor Engine/Thruster Test 04/15/2021
https://www.youtube.com/watch?v=Wa7TPCjgRHk (https://www.youtube.com/watch?v=Wa7TPCjgRHk)
SpaceX McGregor Thruster Test #1 05/04/2021
https://www.youtube.com/watch?v=XwT76nm_gNo (https://www.youtube.com/watch?v=XwT76nm_gNo)
SpaceX McGregor Thruster Test #2 05/04/2021
https://www.youtube.com/watch?v=cK579HjnlhY (https://www.youtube.com/watch?v=cK579HjnlhY)
SpaceX McGregor Thruster Test #1 05/10/2021(audio only no visuals)
https://www.youtube.com/watch?v=D9OGjr24mO8 (https://www.youtube.com/watch?v=D9OGjr24mO8)
SpaceX McGregor Thruster Test #2 05/10/2021(audio only no visuals)
https://www.youtube.com/watch?v=8P8qXwxPQH8&t=138s (https://www.youtube.com/watch?v=8P8qXwxPQH8&t=138s)
SpaceX McGregor Thruster Test 05/12/2021(audio only no visuals)
https://www.youtube.com/watch?v=ThvCrYfw0ow (https://www.youtube.com/watch?v=ThvCrYfw0ow)
These bursts are SO much louder than Raptor or Merlin tests. Although they've all been short, they're VERY impressive
Interesting comment from the person filming those tests:QuoteThese bursts are SO much louder than Raptor or Merlin tests. Although they've all been short, they're VERY impressive
Interesting comment from the person filming those tests:QuoteThese bursts are SO much louder than Raptor or Merlin tests. Although they've all been short, they're VERY impressive
Guys aside mine stupid pump idea. Witch lambda will they run MRCS? Fuel rich or oxygen rich? I would imagine heat for those thrusters would not be such issue due its impulse nature and not "sustained" heat flux. Any thoughts
Near the Raptor test stands is a facility that SpaceX is currently using to test Starship and Super Heavy RCS thrusters.
On his weekly flight, Gary Blair spotted the potential test stand for these hot gas thrusters used to steer the ship and booster to their destinations.
Super Heavy Forward Dome on the Sleeving Stand and Skirt Moved Around
Super Heavy Forward Dome on the Sleeving Stand and Skirt Moved Around
I assume that the photos in the quoted post show the hot gas thrusters.
What can we deduce from those photos?
Three “chambers” with two large pipes and two small pipes. LOx and liquid CH4? (or already gaseous?) and the smaller ones could perhaps be for a pilot light of sorts?
I could definitely also see these used in “cold gas” mode for minimum impulse bit, where the propellants are simply not ignited, but I have no knowledge or experience in this field so what do I know.
I am a little surprised that there is no casing around the RCS unit. Some of the elements look rather delicate, and I am wondering, whether they would survive a supersonic reentry of the booster.Why assume this is the finished article? It would seem obvious to me they'll add thruster and raceway covers etc later on.
I am a little surprised that there is no casing around the RCS unit. Some of the elements look rather delicate, and I am wondering, whether they would survive a supersonic reentry of the booster.I always find these type of comments amusing. It’s as if the boys and girls at SpaceX are new to this spaceflight stuff and know nothing about hypersonic Re entry.
Interesting comment from the person filming those tests:QuoteThese bursts are SO much louder than Raptor or Merlin tests. Although they've all been short, they're VERY impressive
Direction can play a large part. I was 1 mile from a 25k methane engine that was firing perpendicular to me, and you couldn't hear it over people talking; but a 1k alcohol engine at the same distance 100 feet in the air sounded like a jet taking off.Interesting comment from the person filming those tests:QuoteThese bursts are SO much louder than Raptor or Merlin tests. Although they've all been short, they're VERY impressive
How is that even possible? Some sort of pressure density function? Higher pressure at small flow is louder than lower pressure at huge flow?
https://twitter.com/elonmusk/status/1407969457411067905
So the hot-gas thrusters have been:
- Added for Starship flip
- Removed for Starship flip (Raptors only)
- Re-added for Starship in-orbit ops (and possibly Lunar Starship)
- Added to Super Heavy
- Removed from Super Heavy
https://twitter.com/elonmusk/status/1407969457411067905
So the hot-gas thrusters have been:
- Added for Starship flip
- Removed for Starship flip (Raptors only)
- Re-added for Starship in-orbit ops (and possibly Lunar Starship)
- Added to Super Heavy
- Removed from Super Heavy
Which is where you need them. Although I do wonder about the speed it takes for Super Heavy to swing around and do a boostback burn on methox vs nitrogen. I get that for the first orbital test the booster's going to be ending up in the drink but every second before reigniting those engines is hundreds more meters downrange.
They presumably have at least two more SN20 style tests in the works, given how they've run their testing to date. They'd still have those opportunities to flight test the Methox RCS ahead of a catch attempt.
I suspect Elon is ruthlessly constraining the scope of orbital launch #1 to minimise schedule delays, and any non-trivial attempts to improve landing accuracy have been rejected.Which is where you need them. Although I do wonder about the speed it takes for Super Heavy to swing around and do a boostback burn on methox vs nitrogen. I get that for the first orbital test the booster's going to be ending up in the drink but every second before reigniting those engines is hundreds more meters downrange.
They presumably have at least two more SN20 style tests in the works, given how they've run their testing to date. They'd still have those opportunities to flight test the Methox RCS ahead of a catch attempt.
Of course. The best part is no part. The best launch vehicle is a steel bulkhead atop a shaft with a nuclear weapon at the bottom 8)I suspect Elon is ruthlessly constraining the scope of orbital launch #1 to minimise schedule delays, and any non-trivial attempts to improve landing accuracy have been rejected.Which is where you need them. Although I do wonder about the speed it takes for Super Heavy to swing around and do a boostback burn on methox vs nitrogen. I get that for the first orbital test the booster's going to be ending up in the drink but every second before reigniting those engines is hundreds more meters downrange.
They presumably have at least two more SN20 style tests in the works, given how they've run their testing to date. They'd still have those opportunities to flight test the Methox RCS ahead of a catch attempt.
I bet there are dozens of conversations a day along the lines of...
Engineer: "we could test the microconflagulator on the orbital flight by just adding..."
Elon: "No"
Sorry, I didn't mean to imply that there would never be RCS on it. Just that Elon could well be saying "not for launch #1" a lot.Of course. The best part is no part. The best launch vehicle is a steel bulkhead atop a shaft with a nuclear weapon at the bottom 8)I suspect Elon is ruthlessly constraining the scope of orbital launch #1 to minimise schedule delays, and any non-trivial attempts to improve landing accuracy have been rejected.Which is where you need them. Although I do wonder about the speed it takes for Super Heavy to swing around and do a boostback burn on methox vs nitrogen. I get that for the first orbital test the booster's going to be ending up in the drink but every second before reigniting those engines is hundreds more meters downrange.
They presumably have at least two more SN20 style tests in the works, given how they've run their testing to date. They'd still have those opportunities to flight test the Methox RCS ahead of a catch attempt.
I bet there are dozens of conversations a day along the lines of...
Engineer: "we could test the microconflagulator on the orbital flight by just adding..."
Elon: "No"
So the hot-gas thrusters have been:
- Added for Starship flip
- Removed for Starship flip (Raptors only)
- Re-added for Starship in-orbit ops (and possibly Lunar Starship)
- Added to Super Heavy
- Removed from Super Heavy
Adding and removing a paper engine vs. adding and removing a now actual physical engine (not the case until the last few months).
So the hot-gas thrusters have been:
- Added for Starship flip
- Removed for Starship flip (Raptors only)
- Re-added for Starship in-orbit ops (and possibly Lunar Starship)
- Added to Super Heavy
- Removed from Super Heavy
A change in operational design vs a change in one prototype to reduce the amount of variables. Completely different, unrelated things.
Adding and removing a paper engine vs. adding and removing a now actual physical engine (not the case until the last few months).
So the hot-gas thrusters have been:
- Added for Starship flip
- Removed for Starship flip (Raptors only)
- Re-added for Starship in-orbit ops (and possibly Lunar Starship)
- Added to Super Heavy
- Removed from Super Heavy
A change in operational design vs a change in one prototype to reduce the amount of variables. Completely different, unrelated things.
Adding and removing a paper engine vs. adding and removing a now actual physical engine (not the case until the last few months).They habe the time and the tools to do a test installation on flight hardware.
So the hot-gas thrusters have been:
- Added for Starship flip
- Removed for Starship flip (Raptors only)
- Re-added for Starship in-orbit ops (and possibly Lunar Starship)
- Added to Super Heavy
- Removed from Super Heavy
Somwhat.
Nothing to see here.
A change in operational design vs a change in one prototype to reduce the amount of variables. Completely different, unrelated things.
"Any insufficiently flight-ready hardware is indistinguishable from a mass-simulator".Adding and removing a paper engine vs. adding and removing a now actual physical engine (not the case until the last few months).
So the hot-gas thrusters have been:
- Added for Starship flip
- Removed for Starship flip (Raptors only)
- Re-added for Starship in-orbit ops (and possibly Lunar Starship)
- Added to Super Heavy
- Removed from Super Heavy
A change in operational design vs a change in one prototype to reduce the amount of variables. Completely different, unrelated things.
Perhaps it's a fit check with a non-flight unit. They stacked and unstacked an entire booster a couple months ago.
"Any insufficiently flight-ready hardware is indistinguishable from a mass-simulator".Adding and removing a paper engine vs. adding and removing a now actual physical engine (not the case until the last few months).
So the hot-gas thrusters have been:
- Added for Starship flip
- Removed for Starship flip (Raptors only)
- Re-added for Starship in-orbit ops (and possibly Lunar Starship)
- Added to Super Heavy
- Removed from Super Heavy
A change in operational design vs a change in one prototype to reduce the amount of variables. Completely different, unrelated things.
Perhaps it's a fit check with a non-flight unit. They stacked and unstacked an entire booster a couple months ago.
On the igniter, it looks like they haven't hooked up the gox line yet, so that will be something to watch out for. The line that is attached looks like it taps off the fuel inlet and has no valve between it and the igniter, so they might be doing a fuel lead and lag with the fuel always running through the igniter as a purge.Do they need a GOX line in the igniter?