Author Topic: Deep Space Gateway Power/Propulsion RFI  (Read 20587 times)

Offline TrevorMonty

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #80 on: 01/20/2018 11:05 PM »
Orion does not have enough propulsive capability to enter and return from LLO.

I actually requested more information on the Orion delta-v front in another thread, the discussion on which starts here.
This is from memory havn't confirmed it, Orion is about 1800m/s.
« Last Edit: 01/20/2018 11:09 PM by TrevorMonty »

Offline Steven Pietrobon

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #81 on: 01/21/2018 12:16 AM »
Orion does not have enough propulsive capability to enter and return from LLO.

Yes, that's true. It does have enough delta-V to leave LLO though. An EUS designed to last the three day journey to the Moon could do LLO insertion with Orion (as well as an LM on a separate mission).
« Last Edit: 01/21/2018 12:17 AM by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Steven Pietrobon

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #82 on: 01/21/2018 12:19 AM »
This is from memory havn't confirmed it, Orion is about 1800m/s.

Its less than that. I calculated 1227 m/s.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Proponent

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #83 on: 01/22/2018 01:02 PM »
The attached NASAfacts sheet from 2011 indicates a delta-V of 4920 ft/s, i.e., 1500 m/s.

The mass to orbit is quoted as 50,231 lbm, while the SM's propellant load is 17,433 lbm, giving a mass ratio of 1.5315, assuming negligible propellant residuals.  The delta-V of 1500 m/s then in turn implies an effective exhaust velocity of 3518.9 m/s, i.e., a specific impulse of 359 s, which seems unlikely for storable propellants.

I think what's missing in this analysis is that some propellant is burned on the way to orbit, since SLS places Orion only into a transfer orbit with a very low perigee.

EDIT:  The last sentence obviously applies only for some mission profiles.  It would not apply for a cislunar mission launched on a Block 1B SLS.  Since the spec sheet is so old, I wonder whether it may refer to an LEO mission launched by Ares I.
« Last Edit: 01/22/2018 03:59 PM by Proponent »

Offline hektor

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #84 on: 01/22/2018 01:26 PM »
The attached NASAfacts sheet from 2011 indicates a delta-V of 4920 ft/s, i.e., 1500 m/s.

The mass to orbit is quoted as 50,231 lbm, while the SM's propellant load is 17,433 lbm, giving a mass ratio of 1.5315, assuming negligible propellant residuals.  The delta-V of 1500 m/s then in turn implies an effective exhaust velocity of 3518.9 m/s, i.e., a specific impulse of 359 s, which seems unlikely for storable propellants.

I think what's missing in this analysis is that some propellant is burned on the way to orbit, since SLS places Orion only into a transfer orbit with a very low perigee.

Wikipedia gives 316 s for the OMS Engine, if this figure is correct it would be closer to 1200 m/s as indicated above
« Last Edit: 01/22/2018 01:28 PM by hektor »

Offline MaxTeranous

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #85 on: 01/22/2018 01:27 PM »
The attached NASAfacts sheet from 2011 indicates a delta-V of 4920 ft/s, i.e., 1500 m/s.

The mass to orbit is quoted as 50,231 lbm, while the SM's propellant load is 17,433 lbm, giving a mass ratio of 1.5315, assuming negligible propellant residuals.  The delta-V of 1500 m/s then in turn implies an effective exhaust velocity of 3518.9 m/s, i.e., a specific impulse of 359 s, which seems unlikely for storable propellants.

I think what's missing in this analysis is that some propellant is burned on the way to orbit, since SLS places Orion only into a transfer orbit with a very low perigee.

How on earth does SLS not have the juice to put Orion into a decent orbit?

Offline Proponent

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #86 on: 01/22/2018 02:16 PM »
SLS has the juice.  The idea is that you don't want SLS itself going into orbit, because then you don't know where it will re-enter.  That's why Orion has to provide a bit of its own delta-V to reach a stable orbit.

Offline brickmack

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #87 on: 01/22/2018 04:31 PM »
You're confusing the SLS Core stage with iCPS/EUS. The former stages slightly suborbital, the latter reaches a circular parking orbit first and then performs TLI, and then completes a disposal burn afterwards

Offline Proponent

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #88 on: 01/23/2018 02:07 AM »
You're confusing the SLS Core stage with iCPS/EUS. The former stages slightly suborbital, the latter reaches a circular parking orbit first and then performs TLI, and then completes a disposal burn afterwards

Yes, indeed, I am.  Thank you.

Online speedevil

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #89 on: Today at 01:09 AM »
DSG - if you squint a lot, looks moderately like a modern high power GEO comsat with a little more fuel and engines.

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