Author Topic: SpaceX Starship/Super Heavy Engineering General Thread 5  (Read 91811 times)

Online Chris Bergin

New thread (Thread 5)

Thread 1:
Starship (BFS) Engineering Thread (#dearMoon edition + Musk Stainless Update)
https://forum.nasaspaceflight.com/index.php?topic=46395.0

Thread 2:
https://forum.nasaspaceflight.com/index.php?topic=47052.0

Thread 3:
https://forum.nasaspaceflight.com/index.php?topic=48757.0

Thread 4:
https://forum.nasaspaceflight.com/index.php?topic=49622.0

L2 Section - intense level:
https://forum.nasaspaceflight.com/index.php?board=60.0

Recent vids:
https://www.youtube.com/@NASASpaceflight/featured

Store:
https://shop.nasaspaceflight.com/

Be on topic. Don't wander into areas already covered on other threads and make sure your post is useful. :)
« Last Edit: 05/09/2023 01:49 pm by Chris Bergin »
Support NSF via L2 -- Help improve NSF -- Site Rules/Feedback/Updates
**Not a L2 member? Whitelist this forum in your adblocker to support the site and ensure full functionality.**

Offline lightleviathan

  • Full Member
  • *
  • Posts: 159
  • Liked: 135
  • Likes Given: 42
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #1 on: 05/09/2023 02:27 pm »
Why would Starship need ullage gas thrusters again?

Offline Lee Jay

  • Elite Veteran
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 8560
  • Liked: 3578
  • Likes Given: 327
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #2 on: 05/09/2023 02:35 pm »
Why would Starship need ullage gas thrusters again?

As opposed to what, exactly?

Offline lightleviathan

  • Full Member
  • *
  • Posts: 159
  • Liked: 135
  • Likes Given: 42
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #3 on: 05/09/2023 03:08 pm »
None? I thought that it didn't in the first place.

Offline Lee Jay

  • Elite Veteran
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 8560
  • Liked: 3578
  • Likes Given: 327
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #4 on: 05/09/2023 03:22 pm »
None? I thought that it didn't in the first place.

Well, it needs a way to control its attitude in space and during entry before atmospheric interface.

Offline Herb Schaltegger

Ullage is to settle liquid at the bottom of the propellant tanks, so that the intakes are covered and liquid/gas are separated prior to engine ignition. Ullage thrusters are not for attitude control per se.
« Last Edit: 05/09/2023 03:24 pm by Herb Schaltegger »
Ad astra per aspirin ...

Offline D_Dom

  • Global Moderator
  • Full Member
  • *****
  • Posts: 655
  • Liked: 481
  • Likes Given: 152
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #6 on: 05/09/2023 03:52 pm »
According to merriam-webster.com;
ullage: [noun] the amount that a container (such as a tank or cask) lacks of being full.

In this case the tank contains a cryogenic liquid of variable amount. Ullage is the space not occupied by the liquid. Ullage gas fills that space due to boiloff, the pressure can be calculated as detailed in the linked NASA document.  https://ntrs.nasa.gov/api/citations/20000025232/downloads/20000025232.pdf

Ullage settling is required in low gravity to ensure the liquid propellant is consistently available to the tank inlet. You do not want the liquid floating around, you want it to "settle" into the area surrounding the inlet. Thrusters are used for this maneuver, typically requires a short duration burst of low power. Once a main engine is running the "settling" thrusters can be cutoff.

Ullage thrusters can take advantage of the gas pressure generated by boiloff of the propellant. Elon has mentioned using these thrusters for attitude control. I will have a look to try to find a link
Space is not merely a matter of life or death, it is considerably more important than that!

Offline Lee Jay

  • Elite Veteran
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 8560
  • Liked: 3578
  • Likes Given: 327
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #7 on: 05/09/2023 03:56 pm »
Ullage is to settle liquid at the bottom of the propellant tanks, so that the intakes are covered and liquid/gas are separated prior to engine ignition. Ullage thrusters are not for attitude control per se.

Ullage thrusters aren't, but you can use ullage gas for other low-power thrusters.

Offline TheRadicalModerate

  • Senior Member
  • *****
  • Posts: 4314
  • Tampa, FL
  • Liked: 3237
  • Likes Given: 634
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #8 on: 05/09/2023 10:01 pm »
Quote from: TheRadicalModerate

That sounds like a pretty good solution.

Let's figure out how long it'll last.  If we use Tlox=80K, Tlch4=67K, and stainless steel emissivity of 0.57, then

J = (0.57)*(5.670E-8)*(80-67)⁴ = 9.2E-4W/m

If we use a 0.75m x 13m Starship downcomer, that has 5.7m or 12.7t of LCH4 in it.  Up thread, I calculated that you'd need cooling of roughly 83kJ/kg to take the methane down to its freezing point.  That'd take more than 1000 days to freeze with radiative cooling alone.  Even if we're off by a factor of 2, we're still good.

I'm sure there are sneak conductive pathways that will overwhelm this number, but I'm convinced that this is a non-problem for the time being--as long as the downcomer truly is a double-walled dewar.

You made a mistake in your radiative exchange calculations. It should be:
J = (0.57)*(5.670E-8)*(80⁴-67⁴) which is three orders of magnitude higher. So the 1000 days become 1 day.

Yeah, that's a pretty big mistake.  But it's only one of many.  Let me try again:

LCH4 temperature was wrong, should be about 97K, not 67K.
LOX temperature is still 80K
Stainless steel emissivity is still 0.57.
Radiant emittance j = (0.57)*(5.67E-8)*(97⁴ - 80⁴)=1.5W/m
Downcomer diameter=0.75m, length=13m, so surface area=30.6m, volume=5.7m
LCH4 density=448kg/m, mass in downcomer=2.6t (mistake above!).
LCH4 specific heat (at 97K, not 67K)=34.9J/mol-K = 2181J/kg-K
Heat to be lost before freezing begins=(97-90.7)*2181J*2600kg=35,724,780J
Heat loss from downcomer=(1.5W/m)*30.6m=45.9W
Time before freezing begins=35,724,780J/45.9W=9.0 days

9 days is long enough for any earth orbit mission (and certainly suborbital and orbital test flights), but not long enough for lunar or extended cislunar missions.  I'm back to thinking they need a recirculation line at the bottom of the downcomer, which moves cold LCH4 at the bottom to the top of the tank.  But they don't need it right now.

Offline edzieba

  • Virtual Realist
  • Senior Member
  • *****
  • Posts: 5982
  • United Kingdom
  • Liked: 9153
  • Likes Given: 38
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #9 on: 05/10/2023 01:37 pm »
Quote from: TheRadicalModerate

That sounds like a pretty good solution.

Let's figure out how long it'll last.  If we use Tlox=80K, Tlch4=67K, and stainless steel emissivity of 0.57, then

J = (0.57)*(5.670E-8)*(80-67)⁴ = 9.2E-4W/m

If we use a 0.75m x 13m Starship downcomer, that has 5.7m or 12.7t of LCH4 in it.  Up thread, I calculated that you'd need cooling of roughly 83kJ/kg to take the methane down to its freezing point.  That'd take more than 1000 days to freeze with radiative cooling alone.  Even if we're off by a factor of 2, we're still good.

I'm sure there are sneak conductive pathways that will overwhelm this number, but I'm convinced that this is a non-problem for the time being--as long as the downcomer truly is a double-walled dewar.

You made a mistake in your radiative exchange calculations. It should be:
J = (0.57)*(5.670E-8)*(80⁴-67⁴) which is three orders of magnitude higher. So the 1000 days become 1 day.

Yeah, that's a pretty big mistake.  But it's only one of many.  Let me try again:

LCH4 temperature was wrong, should be about 97K, not 67K.
LOX temperature is still 80K
Stainless steel emissivity is still 0.57.
Radiant emittance j = (0.57)*(5.67E-8)*(97⁴ - 80⁴)=1.5W/m
Downcomer diameter=0.75m, length=13m, so surface area=30.6m, volume=5.7m
LCH4 density=448kg/m, mass in downcomer=2.6t (mistake above!).
LCH4 specific heat (at 97K, not 67K)=34.9J/mol-K = 2181J/kg-K
Heat to be lost before freezing begins=(97-90.7)*2181J*2600kg=35,724,780J
Heat loss from downcomer=(1.5W/m)*30.6m=45.9W
Time before freezing begins=35,724,780J/45.9W=9.0 days

9 days is long enough for any earth orbit mission (and certainly suborbital and orbital test flights), but not long enough for lunar or extended cislunar missions.  I'm back to thinking they need a recirculation line at the bottom of the downcomer, which moves cold LCH4 at the bottom to the top of the tank.  But they don't need it right now.
They already need an anti-geysering solution for initial chill and fill, so that system could be repurposed to continue circulation if required in orbit - either by restarting circulation if a circulatory system is used, or carrying a gas supply in some COPVs if a Helium bubbler is used (not ideal, but small volumes required and can be ground-replenished for any non-BEO flights).

Offline darthguili

  • Member
  • Posts: 31
  • Liked: 65
  • Likes Given: 10
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #10 on: 05/10/2023 02:59 pm »

Yeah, that's a pretty big mistake.  But it's only one of many.  Let me try again:

LCH4 temperature was wrong, should be about 97K, not 67K.
LOX temperature is still 80K
Stainless steel emissivity is still 0.57.
Radiant emittance j = (0.57)*(5.67E-8)*(97⁴ - 80⁴)=1.5W/m
Downcomer diameter=0.75m, length=13m, so surface area=30.6m, volume=5.7m
LCH4 density=448kg/m, mass in downcomer=2.6t (mistake above!).
LCH4 specific heat (at 97K, not 67K)=34.9J/mol-K = 2181J/kg-K
Heat to be lost before freezing begins=(97-90.7)*2181J*2600kg=35,724,780J
Heat loss from downcomer=(1.5W/m)*30.6m=45.9W
Time before freezing begins=35,724,780J/45.9W=9.0 days

9 days is long enough for any earth orbit mission (and certainly suborbital and orbital test flights), but not long enough for lunar or extended cislunar missions.  I'm back to thinking they need a recirculation line at the bottom of the downcomer, which moves cold LCH4 at the bottom to the top of the tank.  But they don't need it right now.

I don't know if you want to go there but adding complexity is that the closer the 97K will get to the 90K, the lower the radiative exchanges. This is why sometimes we have to wait for so long to reach a cold equilibrium during TVAC testing: the temperature curve starts with a nice steep slope only to flattens out when reaching cold.
In my experience though, the parasitic conductive couplings are the ones that will deteriorate the radiative insulation so it's likely the 9 days is less than that.
Slightly off topic but somehow connected, measured insitu transient temperatures of the JWST. Temperatures move slowly, timescale is days.

Offline TheRadicalModerate

  • Senior Member
  • *****
  • Posts: 4314
  • Tampa, FL
  • Liked: 3237
  • Likes Given: 634
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #11 on: 05/10/2023 07:32 pm »

Yeah, that's a pretty big mistake.  But it's only one of many.  Let me try again:

LCH4 temperature was wrong, should be about 97K, not 67K.
LOX temperature is still 80K
Stainless steel emissivity is still 0.57.
Radiant emittance j = (0.57)*(5.67E-8)*(97⁴ - 80⁴)=1.5W/m
Downcomer diameter=0.75m, length=13m, so surface area=30.6m, volume=5.7m
LCH4 density=448kg/m, mass in downcomer=2.6t (mistake above!).
LCH4 specific heat (at 97K, not 67K)=34.9J/mol-K = 2181J/kg-K
Heat to be lost before freezing begins=(97-90.7)*2181J*2600kg=35,724,780J
Heat loss from downcomer=(1.5W/m)*30.6m=45.9W
Time before freezing begins=35,724,780J/45.9W=9.0 days

9 days is long enough for any earth orbit mission (and certainly suborbital and orbital test flights), but not long enough for lunar or extended cislunar missions.  I'm back to thinking they need a recirculation line at the bottom of the downcomer, which moves cold LCH4 at the bottom to the top of the tank.  But they don't need it right now.

I don't know if you want to go there but adding complexity is that the closer the 97K will get to the 90K, the lower the radiative exchanges. This is why sometimes we have to wait for so long to reach a cold equilibrium during TVAC testing: the temperature curve starts with a nice steep slope only to flattens out when reaching cold.
In my experience though, the parasitic conductive couplings are the ones that will deteriorate the radiative insulation so it's likely the 9 days is less than that.
Slightly off topic but somehow connected, measured insitu transient temperatures of the JWST. Temperatures move slowly, timescale is days.

Yeah, that's a good point that there will be some exponential decay in radiative heat transfer as the temperature drops.  But the operating temperature of the LOX is far enough below the freezing point of the LCH4 that I don't think you'll get a substantial lengthening of the time before you have to worry about freezing.

I agree that sneak conductive pathways are likely to dominate, and <9 days is likely.  Still, I think it's unlikely that this will change the overall "earth orbit missions OK, BEO missions not" conclusion.
« Last Edit: 05/10/2023 07:32 pm by TheRadicalModerate »

Offline TheRadicalModerate

  • Senior Member
  • *****
  • Posts: 4314
  • Tampa, FL
  • Liked: 3237
  • Likes Given: 634
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #12 on: 05/10/2023 07:34 pm »
Quote from: TheRadicalModerate

That sounds like a pretty good solution.

Let's figure out how long it'll last.  If we use Tlox=80K, Tlch4=67K, and stainless steel emissivity of 0.57, then

J = (0.57)*(5.670E-8)*(80-67)⁴ = 9.2E-4W/m

If we use a 0.75m x 13m Starship downcomer, that has 5.7m or 12.7t of LCH4 in it.  Up thread, I calculated that you'd need cooling of roughly 83kJ/kg to take the methane down to its freezing point.  That'd take more than 1000 days to freeze with radiative cooling alone.  Even if we're off by a factor of 2, we're still good.

I'm sure there are sneak conductive pathways that will overwhelm this number, but I'm convinced that this is a non-problem for the time being--as long as the downcomer truly is a double-walled dewar.

You made a mistake in your radiative exchange calculations. It should be:
J = (0.57)*(5.670E-8)*(80⁴-67⁴) which is three orders of magnitude higher. So the 1000 days become 1 day.

Yeah, that's a pretty big mistake.  But it's only one of many.  Let me try again:

LCH4 temperature was wrong, should be about 97K, not 67K.
LOX temperature is still 80K
Stainless steel emissivity is still 0.57.
Radiant emittance j = (0.57)*(5.67E-8)*(97⁴ - 80⁴)=1.5W/m
Downcomer diameter=0.75m, length=13m, so surface area=30.6m, volume=5.7m
LCH4 density=448kg/m, mass in downcomer=2.6t (mistake above!).
LCH4 specific heat (at 97K, not 67K)=34.9J/mol-K = 2181J/kg-K
Heat to be lost before freezing begins=(97-90.7)*2181J*2600kg=35,724,780J
Heat loss from downcomer=(1.5W/m)*30.6m=45.9W
Time before freezing begins=35,724,780J/45.9W=9.0 days

9 days is long enough for any earth orbit mission (and certainly suborbital and orbital test flights), but not long enough for lunar or extended cislunar missions.  I'm back to thinking they need a recirculation line at the bottom of the downcomer, which moves cold LCH4 at the bottom to the top of the tank.  But they don't need it right now.
They already need an anti-geysering solution for initial chill and fill, so that system could be repurposed to continue circulation if required in orbit - either by restarting circulation if a circulatory system is used, or carrying a gas supply in some COPVs if a Helium bubbler is used (not ideal, but small volumes required and can be ground-replenished for any non-BEO flights).

In general, I suspect that the finished product will have a fair amount of plumbing that's driven by relatively low-flow electric pumps.

Offline TheRadicalModerate

  • Senior Member
  • *****
  • Posts: 4314
  • Tampa, FL
  • Liked: 3237
  • Likes Given: 634
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #13 on: 05/10/2023 07:50 pm »
Quote from: warp99
....  One option is to store ullage gas in COPVs using electric pumps during powered flight and then release to the tanks just before engine relight. ...

- Autogenous gases tapped off of the Raptor engine have a pressure of over 6000 psi. They are regulated down to lower pressure to feed the main tanks. A high pressure line could feed COPVs. No electric pump needed.

John

Have you changed your mind about the need for low-velocity pumps to move liquid from the mains to the COPVs, where it can be heated up to supercritical?

Autogenous tap-off will work when the next need for COPV gases (cold/warm-gas thrusters, methox combustion thrusters, spin-up gases, pre-flight ullage pressurization--it's a long list) will occur fairly soon after a main engine burn, but will it be adequate for a maneuver that occurs months or years after the last main engine burn?

Looks like 408bar is well above the critical pressure for both O2 and CH4, so maybe even if the COPVs cool down to ambient, a compressible liquid might be good enough for our purposes?

Offline livingjw

  • Senior Member
  • *****
  • Posts: 2363
  • New World
  • Liked: 5857
  • Likes Given: 2887
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #14 on: 05/11/2023 01:28 am »
Quote from: warp99
....  One option is to store ullage gas in COPVs using electric pumps during powered flight and then release to the tanks just before engine relight. ...

- Autogenous gases tapped off of the Raptor engine have a pressure of over 6000 psi. They are regulated down to lower pressure to feed the main tanks. A high pressure line could feed COPVs. No electric pump needed.

John

Have you changed your mind about the need for low-velocity pumps to move liquid from the mains to the COPVs, where it can be heated up to supercritical?

Autogenous tap-off will work when the next need for COPV gases (cold/warm-gas thrusters, methox combustion thrusters, spin-up gases, pre-flight ullage pressurization--it's a long list) will occur fairly soon after a main engine burn, but will it be adequate for a maneuver that occurs months or years after the last main engine burn?

Looks like 408bar is well above the critical pressure for both O2 and CH4, so maybe even if the COPVs cool down to ambient, a compressible liquid might be good enough for our purposes?

- No, I have not changed my mind. Pumping LCH4 and LOx into empty or low pressure COPVs and heating them up will be needed to recharge after weeks, months or years.

- I just wanted to make it clear that it is not needed for the booster or for short stays in orbit.

John

Offline Hooperball

  • Member
  • Posts: 45
  • Liked: 5
  • Likes Given: 1
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #15 on: 05/11/2023 12:45 pm »
The question was about the requirement of ullage thrusters. Please bear with me, I have never heard of a "low velocity 410 bar (6000 PSI) pumps" or a COPV becoming an FCOPV (Fired Composite Overwrapped Pressure Vessel) with free electrical power or a on orbit meth/Lox boiler and burner assembly to heat and store thermal energy for no apparent reason for supercritical (beyond triple point) pressurization systems? I logged in for the first time in ten years just to say WOW.
   
Please consider the fact; there are no ullage thrusters, stage separation thrusters, or booster retrograde thrusters utilized during staging.

They painted the RP1 section of the Falcon Heavy second stage to prevent the kerosene from solidifying. Not the LOx section.   

Boil off and recovery of methane and oxygen is the biggest problem for long duration flights and will require compressors, plus power, plus heat exchangers to maintain the propellent onboard.  The Saturn-Apollo 3rd stages actually increased dV and altitude prior to TLI from boil off venting alone in the order of a ~25-50 m/s per orbit.

With the excess of boil off and the resulting PRESSURE, Spacex in sequence can and will use the resulting; tank pressure chill-in venting thrust, followed by preburner "spin prime" thrust to provide tank settling prior to preburner ignition. The COPV's will use their pre charged nitrogen from the earth to spool up the turbines just like the inner engines on the booster during boost back.

ULLAGE is the measured distance from the top of the tank to the surface of the fluid.
INNAGE is the measured distance from the surface of the fluid to the bottom of the tank.

Ares-1X never had any of these issues to contend with...

Hoop

Offline livingjw

  • Senior Member
  • *****
  • Posts: 2363
  • New World
  • Liked: 5857
  • Likes Given: 2887
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #16 on: 05/11/2023 01:59 pm »

.... I have never heard of a "low velocity 410 bar (6000 PSI) pumps"

.... a COPV becoming an FCOPV (Fired Composite Overwrapped Pressure Vessel)

.... with free electrical power

....on orbit meth/Lox boiler and burner assembly to heat and store thermal energy for no apparent reason....

.... COPV's will use their pre charged nitrogen from the earth to spool up the turbines just like the inner engines on the booster during boost back.


- I believe he meant low pressure pump. The concept we are talking about was to recharge GCH4 and GOx COPVs after a long duration stay (weeks, months) in orbit or on planet. The process would be:
1) given empty GCH4 and GOx COPVs, main tanks with LCH4 and LOx, and solar or APU electrical power.
2) pump LCH4 and LOx into respective empty (low pressure) COPVs.
3) electrically heat to gasify and pressurize. You now have what you need to spin up your engines without high press GN2.

John
« Last Edit: 05/11/2023 02:00 pm by livingjw »

Offline Hog

  • Senior Member
  • *****
  • Posts: 2843
  • Woodstock
  • Liked: 1698
  • Likes Given: 6849
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #17 on: 05/11/2023 04:59 pm »
The question was about the requirement of ullage thrusters. Please bear with me, I have never heard of a "low velocity 410 bar (6000 PSI) pumps" or a COPV becoming an FCOPV (Fired Composite Overwrapped Pressure Vessel) with free electrical power or a on orbit meth/Lox boiler and burner assembly to heat and store thermal energy for no apparent reason for supercritical (beyond triple point) pressurization systems? I logged in for the first time in ten years just to say WOW.
   
Please consider the fact; there are no ullage thrusters, stage separation thrusters, or booster retrograde thrusters utilized during staging.

They painted the RP1 section of the Falcon Heavy second stage to prevent the kerosene from solidifying. Not the LOx section.   

Boil off and recovery of methane and oxygen is the biggest problem for long duration flights and will require compressors, plus power, plus heat exchangers to maintain the propellent onboard.  The Saturn-Apollo 3rd stages actually increased dV and altitude prior to TLI from boil off venting alone in the order of a ~25-50 m/s per orbit.

With the excess of boil off and the resulting PRESSURE, Spacex in sequence can and will use the resulting; tank pressure chill-in venting thrust, followed by preburner "spin prime" thrust to provide tank settling prior to preburner ignition. The COPV's will use their pre charged nitrogen from the earth to spool up the turbines just like the inner engines on the booster during boost back.

ULLAGE is the measured distance from the top of the tank to the surface of the fluid.
INNAGE is the measured distance from the surface of the fluid to the bottom of the tank.

Ares-1X never had any of these issues to contend with...

Hoop
Hi Hooperball, nice to see you around posting again.  I enjoyed your posts from over a decade ago!


xxxxxxx
If ULLAGE is the measured distance from the top of the tank to the surface of the fluid, is the term "ULLAGE SPACE" a correct method to describe its volume, or would you simply state "ullage volume"?
Paul

Offline TheRadicalModerate

  • Senior Member
  • *****
  • Posts: 4314
  • Tampa, FL
  • Liked: 3237
  • Likes Given: 634
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #18 on: 05/12/2023 04:53 am »
The question was about the requirement of ullage thrusters. Please bear with me, I have never heard of a "low velocity 410 bar (6000 PSI) pumps" or a COPV becoming an FCOPV (Fired Composite Overwrapped Pressure Vessel) with free electrical power or a on orbit meth/Lox boiler and burner assembly to heat and store thermal energy for no apparent reason for supercritical (beyond triple point) pressurization systems? I logged in for the first time in ten years just to say WOW.

What John said:  Vent the COPV, use low velocity, low power electric pumps to flow liquid from the mains into the COPV, seal 'em, then heat 'em up.  But if you can fill them via autogenous tap-off when the Raptors are running, that'll give you a shorter cycle time.

Tap-off may work fine for earth orbit missions, maybe even for short cislunar missions.  But I doubt it works for leaving a lunar Starship in NRHO for months or years, nor does it necessarily work for surface missions.

I doubt any of this is implemented yet.  It's not needed for the minimum viable product, which is a Starship that can complete its test flights, followed shortly thereafter by a sequence of flights that deploy Starlinks before completing additional EDL and refueling tests.  But it's going to be needed before Option A is complete.

Quote
Please consider the fact; there are no ullage thrusters, stage separation thrusters, or booster retrograde thrusters utilized during staging.

That's true, but there will have to be ullage thrusters for prop transfer.  It's possible that only the depot needs them, although that'll be an interesting attitude control problem.  Starship will also need RCS for attitude control and low-delta-v TCMs.  A lot of different calculations cast doubt on whether warm-ish non-combusting gas directly from the mains will be good enough.  Also, if there's a lesson to be learned from the first launch, it's that the lunar Starship is really, really, really going to need waist thrusters for landing and probably ascent, and those will almost certainly have to be pressure-fed combusting thrusters.

Quote
They painted the RP1 section of the Falcon Heavy second stage to prevent the kerosene from solidifying. Not the LOx section.

That's because it only has a 10 hour loiter life.  But I'm still curious how they keep the RP-1 in the downcomer from freezing.  Seems like there has to be a dewar involved, but even then it's a big temperature difference.

Quote
With the excess of boil off and the resulting PRESSURE, Spacex in sequence can and will use the resulting; tank pressure chill-in venting thrust, followed by preburner "spin prime" thrust to provide tank settling prior to preburner ignition. The COPV's will use their pre charged nitrogen from the earth to spool up the turbines just like the inner engines on the booster during boost back.

I suspect that the booster will indeed just use pre-charged COPVs filled with N2 or He for almost everything, and warm-ish gas thrusters may be adequate for the amount of attitude control needed.  But for Starship, nobody has ever attempted to do cryogenic prop management for loiter times of weeks or months.  And you can't get the volume of gas you need with boil-off that has to vent a 8bar.  Energy has to be added somewhere to generate a lot more pV.

Offline gsa

  • Full Member
  • *
  • Posts: 124
  • Moscow, Russia
  • Liked: 120
  • Likes Given: 135
Re: SpaceX Starship/Super Heavy Engineering General Thread 5
« Reply #19 on: 05/12/2023 12:27 pm »
They painted the RP1 section of the Falcon Heavy second stage to prevent the kerosene from solidifying. Not the LOx section.
That's because it only has a 10 hour loiter life.  But I'm still curious how they keep the RP-1 in the downcomer from freezing.  Seems like there has to be a dewar involved, but even then it's a big temperature difference.
In the Falcon the RP-1 tank is below the LOX tank. There is no kerosine in the downcomer.

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
0