Author Topic: NASA Gateway Lunar Lander  (Read 39005 times)

Offline jongoff

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Re: NASA Gateway Lunar Lander
« Reply #240 on: 02/15/2019 09:24 pm »
Disagree - station-keeping propellant for an LLO station would eat your lunch.  Plus it disallows using the station as a staging point for any other BEO missions.

On the first point, not necessarily -- it depends strongly on how low of an LLO we're talking about. Sure down at 50-100km it's an issue, but if you went with say a 500km LLO, it's manageable.

It is true that a LLO gateway is more optimized for lunar surface ops than other BLEO missions, but the Moon is NASA's near- and medium-term focus. I don't think hamstringing their near-term focus for something you could add later makes sense.

~Jon

Offline sevenperforce

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Re: NASA Gateway Lunar Lander
« Reply #241 on: 02/15/2019 09:32 pm »
Disagree - station-keeping propellant for an LLO station would eat your lunch.  Plus it disallows using the station as a staging point for any other BEO missions.

On the first point, not necessarily -- it depends strongly on how low of an LLO we're talking about. Sure down at 50-100km it's an issue, but if you went with say a 500km LLO, it's manageable.

It is true that a LLO gateway is more optimized for lunar surface ops than other BLEO missions, but the Moon is NASA's near- and medium-term focus. I don't think hamstringing their near-term focus for something you could add later makes sense.

~Jon
Why not an 86-degree frozen orbit? It's nearly polar so you have excellent access.

Offline sevenperforce

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Re: NASA Gateway Lunar Lander
« Reply #242 on: 02/15/2019 10:06 pm »
Something I have not yet seen in any proposals but that occurred to me today....

Has anyone ever proposed using a wet-workshop airlock? Wet workshops aren't particularly useful for space station applications, but if all you need is a separate room, that's pretty much exactly what you'd need.

You'd have your reusable main crew capsule built with the docking port in the floor, rather than the ceiling, and you'd dock feet-first at the gateway. The descent stage would have a docking port welded to the top of a central, cylindrical fuel tank, and that tank would have a hatch cut in one side.

After landing, you'd purge the hydrogen tank with nitrogen, vent in residual LOX to bring it up to breathable levels, then open the floor hatch and you've got your airlock. Close the hatch and blast away at the end of the mission.
Used KSP to throw up a simple mockup of a wet-workshop airlock....

Offline jongoff

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Re: NASA Gateway Lunar Lander
« Reply #243 on: 02/15/2019 10:18 pm »
Disagree - station-keeping propellant for an LLO station would eat your lunch.  Plus it disallows using the station as a staging point for any other BEO missions.

On the first point, not necessarily -- it depends strongly on how low of an LLO we're talking about. Sure down at 50-100km it's an issue, but if you went with say a 500km LLO, it's manageable.

It is true that a LLO gateway is more optimized for lunar surface ops than other BLEO missions, but the Moon is NASA's near- and medium-term focus. I don't think hamstringing their near-term focus for something you could add later makes sense.

~Jon
Why not an 86-degree frozen orbit? It's nearly polar so you have excellent access.

You'd still have to do some level of a plane change to get to a polar site. Frozen orbits are overrated, IMO. At least for this application.

~Jon

Offline A_M_Swallow

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Re: NASA Gateway Lunar Lander
« Reply #244 on: 02/15/2019 11:07 pm »

Disagree - station-keeping propellant for an LLO station would eat your lunch.  Plus it disallows using the station as a staging point for any other BEO missions.

It might be simpler and more flexible just to have a reusable inter-orbital tug (maybe just a duplicate of the lander descent stage, sans landing hardware).

No. The LOP-G will have a ion thruster so it will need no more than one and a half tonnes of Xenon for station keeping (normally less).

The Advanced Electric Propulsion System (AEPS) thrusters have an Isp of 2,600 s.
max LLO station keeping delta-v 400 m/s (including desaturation)
mf = m1(exp(deltav/(Isp*g)) - 1)

m1 = gateway mass + Orion mass + three stage lander + lander fuel + lander cargo
   = about 30 tonne + 26 tonne + 16 tonne + 10 tonne + 12 tonne
   = 94 tonne (94,000 kg)

mf = 94000 * (exp(400/(2600 * 9.81)) -1) = 1,486 kg

So the worst case is the LOP-G would require one and a half metric tons of Xenon a year.

Using the 150 m/s delta-v

mf = 94000 * (exp(150/(2600 * 9.81)) -1) = 554 kg

edit: correct to 554 kg
« Last Edit: 02/16/2019 12:04 am by A_M_Swallow »

Offline ncb1397

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Re: NASA Gateway Lunar Lander
« Reply #245 on: 02/15/2019 11:27 pm »

Disagree - station-keeping propellant for an LLO station would eat your lunch.  Plus it disallows using the station as a staging point for any other BEO missions.

It might be simpler and more flexible just to have a reusable inter-orbital tug (maybe just a duplicate of the lander descent stage, sans landing hardware).

No. The LOP-G will have a ion thruster so it will need no more than one and a half tonnes of Xenon for station keeping (normally less).

The Advanced Electric Propulsion System (AEPS) thrusters have an Isp of 2,600 s.
max LLO station keeping delta-v 400 m/s (including desaturation)
mf = m1(exp(deltav/(Isp*g)) - 1)

m1 = gateway mass + Orion mass + three stage lander + lander fuel + lander cargo
   = about 30 tonne + 26 tonne + 16 tonne + 10 tonne + 12 tonne
   = 94 tonne (94,000 kg)

mf = 94000 * (exp(400/(2600 * 9.81)) -1) = 1,486 kg

So the worst case is the LOP-G would require one and a half metric tons of Xenon a year.

Using the 150 m/s delta-v

mf = 94000 * (exp(150/(2600 * 9.81)) -1) = 55.4 kg

554 kg?

Anyways, you have to take into account solar array sizing as well. 1500 kg of matter travelling at 26000 m/s is 140 MWh of energy. Assuming thrust efficiency of 50%, you have to harvest 280 MWh per year. In low lunar orbit, you collect energy for 4380 hours per year (12 * 365). You would need 64 KW(280000 / 4380) arrays for just the propulsion portion only. Call it 100 KW as you have a lot of other loads, gradual degradation and you won't be thrusting 100% of the time and you can't store much. The array would have to be 2-2.5x larger than what NASA is currently planning and you need 2+ more engines.
« Last Edit: 02/15/2019 11:30 pm by ncb1397 »

Offline A_M_Swallow

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Re: NASA Gateway Lunar Lander
« Reply #246 on: 02/16/2019 12:15 am »

554 kg?

Confirm, post corrected. Thank you.
Quote

Anyways, you have to take into account solar array sizing as well. 1500 kg of matter travelling at 26000 m/s is 140 MWh of energy. Assuming thrust efficiency of 50%, you have to harvest 280 MWh per year. In low lunar orbit, you collect energy for 4380 hours per year (12 * 365). You would need 64 KW(280000 / 4380) arrays for just the propulsion portion only. Call it 100 KW as you have a lot of other loads, gradual degradation and you won't be thrusting 100% of the time and you can't store much. The array would have to be 2-2.5x larger than what NASA is currently planning and you need 2+ more engines.

The easiest way of doubling the thrust is to fit the LOP-G with two Power and Propulsion Elements. Where the solar panels would go will have to be decided.

Offline TaurusLittrow

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Re: NASA Gateway Lunar Lander
« Reply #247 on: 02/16/2019 01:52 pm »
Based on the NASA media press conference on 2/14 regarding the lunar landing architecture, the Descent Element and Transfer Vehicle Element will be launched on commercial LVs and each will have a wet mass of 15 mT. The Gateway logistic modules have a 7.6 mT (pressurized and/or unpressurized cargo) requirement.

LV performance plots, from NASA's website, would indicate that FH expendable is the only vehicle capable of fulfilling both roles. Delta IV Heavy and perhaps the FH recovered could meet the logistic payload requirement.

No performance plots were available for NG (2/3 stage) or Vulcan, but informed speculation is welcome.

Offline Markstark

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Offline philw1776

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Re: NASA Gateway Lunar Lander
« Reply #249 on: 02/16/2019 08:53 pm »
Full charts: https://www.nasa.gov/sites/default/files/atoms/files/nasa_hls_baa_industry_forum_14feb2019.pdf

Appreciated

I wonder what does and what does not constitute "credible launch readiness in 202X"?
Criteria?
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Offline TrevorMonty

Re: NASA Gateway Lunar Lander
« Reply #250 on: 02/16/2019 09:29 pm »
How does Descent stage and Transfer stage get from LEO to Gateway?.

At 15mt they can only be delivered to LEO by current commercial LVs. Both are capable of LEO - gateway trip but it'll burn majority of their fuel.

Offline A_M_Swallow

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Re: NASA Gateway Lunar Lander
« Reply #251 on: 02/16/2019 10:10 pm »
How does Descent stage and Transfer stage get from LEO to Gateway?.

At 15mt they can only be delivered to LEO by current commercial LVs. Both are capable of LEO - gateway trip but it'll burn majority of their fuel.

Re-usability requires the stages to be refuelled. So a depot or fuelling tanker or both will need developing and sending to the LOP-G.

Do the 3 stages use the same propellant or different propellants?

Offline AndrewSmith

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Re: NASA Gateway Lunar Lander
« Reply #252 on: 02/16/2019 11:53 pm »

Disagree - station-keeping propellant for an LLO station would eat your lunch.  Plus it disallows using the station as a staging point for any other BEO missions.

It might be simpler and more flexible just to have a reusable inter-orbital tug (maybe just a duplicate of the lander descent stage, sans landing hardware).

No. The LOP-G will have a ion thruster so it will need no more than one and a half tonnes of Xenon for station keeping (normally less).

The Advanced Electric Propulsion System (AEPS) thrusters have an Isp of 2,600 s.
max LLO station keeping delta-v 400 m/s (including desaturation)
mf = m1(exp(deltav/(Isp*g)) - 1)

m1 = gateway mass + Orion mass + three stage lander + lander fuel + lander cargo
   = about 30 tonne + 26 tonne + 16 tonne + 10 tonne + 12 tonne
   = 94 tonne (94,000 kg)

mf = 94000 * (exp(400/(2600 * 9.81)) -1) = 1,486 kg

So the worst case is the LOP-G would require one and a half metric tons of Xenon a year.

Using the 150 m/s delta-v

mf = 94000 * (exp(150/(2600 * 9.81)) -1) = 554 kg

edit: correct to 554 kg

The PPE is thrust limited - its unclear if a 50KW SEP tug can keep up with the intensity and isotropy of the gravity perturbations in LLO. 

Its more likely that the entire LOP-G complex will move between different DRO and NRHO orbits throughout its life - some of which have a fairly high eccentricity (and low perilune) - capable of supporting surface missions with a far lower dV than a DRO-LLO-surface transfer.

Offline A_M_Swallow

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Re: NASA Gateway Lunar Lander
« Reply #253 on: 02/17/2019 03:13 pm »

The PPE is thrust limited - its unclear if a 50KW SEP tug can keep up with the intensity and isotropy of the gravity perturbations in LLO. 

Its more likely that the entire LOP-G complex will move between different DRO and NRHO orbits throughout its life - some of which have a fairly high eccentricity (and low perilune) - capable of supporting surface missions with a far lower dV than a DRO-LLO-surface transfer.

The lunar spacestation complex will need thinking through so we can determine its parts and calculate its mass.

The sort of thrusting in the DRO-LLO orbits can e determined experimentally by sending a simple nanosat to the orbit and seeing what its ion thruster has to do to maintain orbit. NASA could make and launch this in two years.

Offline Prober

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Re: NASA Gateway Lunar Lander
« Reply #254 on: 02/17/2019 04:59 pm »
A modified architecture using existing HW.

 
Goal : Lunar Stay program

 
Prepare a clean landing site for Lunar Stay
Stockpile supplies
Robotic site preparation equipment
 
Transport to Lunar surface

 
A sky crane modified for Lunar operations (soft drop & return to gateway)
for prep supplies (pre-Human transport).

*
https://mars.jpl.nasa.gov/msl/mission/technology/insituexploration/edl/skycrane/

 
the benefits will become self evident

 
Hope you enjoyed the tease, I have so much more :)

 
So many of the contractors would be real happy.



*wrong link
« Last Edit: 02/19/2019 04:24 am by Prober »
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Offline brickmack

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Re: NASA Gateway Lunar Lander
« Reply #255 on: 02/17/2019 05:47 pm »
How does Descent stage and Transfer stage get from LEO to Gateway?.

At 15mt they can only be delivered to LEO by current commercial LVs. Both are capable of LEO - gateway trip but it'll burn majority of their fuel.

FH expendable can send that direct to TLI today. DIVH can send that roughly to GTO today. Single-launch Vulcan can nearly do that to TLI (somewhere between GTO and TLI). New Glenn can send it to somewhere a bit short of GTO.

Offline Zed_Noir

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Re: NASA Gateway Lunar Lander
« Reply #256 on: 02/18/2019 04:42 am »
....
Transport to Lunar surface

 
A sky crane modified for Lunar operations (soft drop & return to gateway)
for prep supplies (pre-Human transport).
....

 ::)
You do realize that the Sky Crane Mars landing system utilizes aero braking and a very large parachute to do most of the deceleration. The brief rocket powered landing phase is for terminal touch down of the rover and the removal of the rover carrier from the landing site.

Offline Steven Pietrobon

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Re: NASA Gateway Lunar Lander
« Reply #257 on: 02/18/2019 05:30 am »
One question I have with NASA's architecture is how the Refuel Element vehicles are disposed of. Just leave them to drift about in NRO?
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline RonM

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Re: NASA Gateway Lunar Lander
« Reply #258 on: 02/18/2019 05:27 pm »
One question I have with NASA's architecture is how the Refuel Element vehicles are disposed of. Just leave them to drift about in NRO?

Design the propellant tanks "wet lab style" so they can be used later. Use a cargo lander to take empty refuel elements down to the surface and use them for additional pressurized volume at a lunar base. Hardware placed in lunar orbit will be a valuable resource.

Of course, there are trade offs. How much would it cost to convert, is there enough usable volume, etc. There will be additional cost to dispose of the refueling elements since deltaV isn't free, so reuse might be viable considering the cost of sending new habitat modules.

Then again, Steven's question might be another sign that Gateway architecture is fundamentally flawed.

Offline ncb1397

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Re: NASA Gateway Lunar Lander
« Reply #259 on: 02/18/2019 07:26 pm »
Disposal will likely be lunar impact - like Lunar Orbiter 1, Lunar Orbiter 2, Lunar Orbiter 3, Lunar Orbiter 4, Lunar Orbiter 5, GRAIL A, GRAIL B, LADEE, LCROSS (2 objects), Lunar Prospector, Ranger 4, Ranger 6, Ranger 7, Ranger 8, Ranger 9, Explorer 35, Explorer 49, Surveyor 2, Surveyor 4, the Apollo-10 LM descent stage, Apollo 11 LM ascent stage, Apollo 12 LM ascent stage, Apollo 14 LM ascent stage, Apollo 15 LM ascent stage, Apollo 16 LM ascent stage, Apollo 17 LM ascent stage, a bunch of Saturn V upper stages, Chandrayaan-1 (did this impact yet?), Chandrayaan-1 Moon Impact Probe, Luna 2, Luna 2 third stage, Luna 5, Luna 7, Luna 8, Luna 10, Luna 11, Luna 12, Luna 14, Luna 15, Luna, 18, Luna 19, Luna 22, Hiten, Hagoromo, SELENE, SMART-1, Chang'e 1.
« Last Edit: 02/18/2019 09:29 pm by ncb1397 »

Tags: lop-g lunar gateway