Author Topic: Deep Space Gateway Power/Propulsion RFI  (Read 36020 times)

Offline theinternetftw

  • Full Member
  • *
  • Posts: 164
    • www.theinternetftw.com
  • Liked: 406
  • Likes Given: 220
Deep Space Gateway Power/Propulsion RFI
« on: 07/20/2017 09:00 PM »
I searched and didn't find any discussion of this, on NSF or anywhere else.  As Chris put his DSG article from June in here, I'm (tentatively) putting this here as well.

https://www.nasa.gov/feature/nasa-power-propulsion-rfi

NASA has issued an RFI on the first DSG module, the PPE (Power Propulsion Element).  Despite the press release being quite threadbare, the RFI itself has a good bit of information in it.

* 24kW of providable power
* 50kW-class SEP engine
* 2000kg-class Xenon tank
* On-orbit refueling of xenon and hydrazine (requests info on green hydrazine drop-in replacements)
* No heavier than 7,500kg (including payload adapter)
* Currently planned to be co-manifested on EM-2

Edit: added a bullet point, attached RFI itself to save a step or two
« Last Edit: 07/20/2017 09:09 PM by theinternetftw »

Online Chris Bergin

« Last Edit: 07/21/2017 07:35 PM by Chris Bergin »

Offline brickmack

  • Full Member
  • ****
  • Posts: 465
  • USA
  • Liked: 174
  • Likes Given: 13
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #2 on: 07/20/2017 10:05 PM »
I wonder why they went with hydrazine RCS instead of xenon. SEP RCS+CMGs is now a well-proven combination. Not enough torque for a station this size? Or not enough for control during docking?
« Last Edit: 07/20/2017 10:05 PM by brickmack »

Offline redliox

  • Full Member
  • ****
  • Posts: 1927
  • Arizona USA
  • Liked: 372
  • Likes Given: 64
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #3 on: 07/20/2017 10:09 PM »
I wonder why they went with hydrazine RCS instead of xenon. SEP RCS+CMGs is now a well-proven combination. Not enough torque for a station this size? Or not enough for control during docking?

Hydrazine is frequently used and, while toxic, is stable and predictable for thrusters.  SEP/xenon will have its moment to shine, but in short hydrazine is fast while xenon is slow.  Xenon would still be used to put the module around the moon, probably some station keeping, whereas hydrazine would be used for crew visit dockings.
"Let the trails lead where they may, I will follow."
-Tigatron

Offline theinternetftw

  • Full Member
  • *
  • Posts: 164
    • www.theinternetftw.com
  • Liked: 406
  • Likes Given: 220
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #4 on: 07/20/2017 10:30 PM »
Thanks Chris.  Check my registration date to marvel at my previous steadfast commitment to lurkerdom :D

Online yg1968

  • Senior Member
  • *****
  • Posts: 9674
  • Liked: 1388
  • Likes Given: 876

Offline Propylox

  • Member
  • Posts: 81
  • Colorado
  • Liked: 6
  • Likes Given: 7
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #6 on: 07/21/2017 03:09 AM »
"Near rectilinear halo orbit" is a non-starter. If you'd like to know more about the impossibility of station keeping, manned habitation and severe constraints on every mission plan it creates, NASA has plenty of papers - oddly pointing this out and concluding we should do it anyways. Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Cislunar Near Rectilinear Halo Orbit for Human Space Exploration - Sept 2016
https://ntrs.nasa.gov/search.jsp?R=20160003078


Is there anything about that image that makes you think it's a good idea or in any way useful? It's a hot mess in the middle of nowhere. Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.
« Last Edit: 07/21/2017 03:11 AM by Propylox »

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #7 on: 07/21/2017 04:18 AM »
{snip}
Is there anything about that image that makes you think it's a good idea or in any way useful? It's a hot mess in the middle of nowhere. Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.

1. Pretty picture.

2. I thought low lunar orbits (LLO) were unstable, requiring between 0-400 m/s of station keeping.

Putting the DSG in LLO would make lunar landing much easier.

I suspect NASA wants to put the DSG in a high lunar orbit to reduce the delta-v needed by the large mass transfer vehicle to go to Mars. However if the DSG only has a 15 year life expectancy then the Mars Transfer Vehicle (MTV) will still be under construction at the end of the Gateway's life. DSG #2 may be the return point for the MTV.

Offline theinternetftw

  • Full Member
  • *
  • Posts: 164
    • www.theinternetftw.com
  • Liked: 406
  • Likes Given: 220
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #8 on: 07/21/2017 04:26 AM »
"Near rectilinear halo orbit" is a non-starter. [...] Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.

Is part of it about wanting a big SEP project in a post-ARM world?  Back-solving from the tech they want to fund?

Offline TrevorMonty

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #9 on: 07/21/2017 05:48 AM »
"Near rectilinear halo orbit" is a non-starter. If you'd like to know more about the impossibility of station keeping, manned habitation and severe constraints on every mission plan it creates, NASA has plenty of papers - oddly pointing this out and concluding we should do it anyways. Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Cislunar Near Rectilinear Halo Orbit for Human Space Exploration - Sept 2016
https://ntrs.nasa.gov/search.jsp?R=20160003078


Is there anything about that image that makes you think it's a good idea or in any way useful? It's a hot mess in the middle of nowhere. Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.
What use is DSG at LLO when no one can visit it. Orion could make it to LLO but it would be oneway trip.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32378
  • Cape Canaveral Spaceport
  • Liked: 11065
  • Likes Given: 329
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #10 on: 07/21/2017 12:53 PM »
{snip}
Is there anything about that image that makes you think it's a good idea or in any way useful? It's a hot mess in the middle of nowhere. Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.

1. Pretty picture.

2. I thought low lunar orbits (LLO) were unstable, requiring between 0-400 m/s of station keeping.

Putting the DSG in LLO would make lunar landing much easier.

I suspect NASA wants to put the DSG in a high lunar orbit to reduce the delta-v needed by the large mass transfer vehicle to go to Mars. However if the DSG only has a 15 year life expectancy then the Mars Transfer Vehicle (MTV) will still be under construction at the end of the Gateway's life. DSG #2 may be the return point for the MTV.

Has nothing to do with MTV

Offline envy887

  • Senior Member
  • *****
  • Posts: 4502
  • Liked: 2439
  • Likes Given: 1367
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #11 on: 07/21/2017 01:43 PM »
{snip}
Is there anything about that image that makes you think it's a good idea or in any way useful? It's a hot mess in the middle of nowhere. Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.

1. Pretty picture.

2. I thought low lunar orbits (LLO) were unstable, requiring between 0-400 m/s of station keeping.

Putting the DSG in LLO would make lunar landing much easier.

I suspect NASA wants to put the DSG in a high lunar orbit to reduce the delta-v needed by the large mass transfer vehicle to go to Mars. However if the DSG only has a 15 year life expectancy then the Mars Transfer Vehicle (MTV) will still be under construction at the end of the Gateway's life. DSG #2 may be the return point for the MTV.

Has nothing to do with MTV

Specifically, the Deep Space Transport (the Mars transfer vehicle) can easily enter and exit LLO.

The problem is Orion cannot enter and then exit LLO, so no infrastructure using Orion will be built or moved there.

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #12 on: 07/21/2017 04:57 PM »
The other item I noticed was max weight for this co-manifested payload showing there is likely going to this orbit with Orion on a SLS-1B only 7.5mt of excess capability. Which also means that the DSG itself will have to weigh no more than 7.5mt. This orbit was probably picked because for other orbits there just was not enough excess capability to have a useful co-manifested payload.

Offline GWH

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #13 on: 07/21/2017 05:13 PM »
The other item I noticed was max weight for this co-manifested payload showing there is likely going to this orbit with Orion on a SLS-1B only 7.5mt of excess capability. Which also means that the DSG itself will have to weigh no more than 7.5mt. This orbit was probably picked because for other orbits there just was not enough excess capability to have a useful co-manifested payload.
Yes mass restrictions seem to be popping up and causing development problems, see links below:
http://russianspaceweb.com/imp-ppb.html#2017

http://russianspaceweb.com/imp-lcub.html

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1006
  • Long Beach, California
  • Liked: 204
  • Likes Given: 591
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #14 on: 07/21/2017 05:47 PM »
The other item I noticed was max weight for this co-manifested payload showing there is likely going to this orbit with Orion on a SLS-1B only 7.5mt of excess capability. Which also means that the DSG itself will have to weigh no more than 7.5mt. This orbit was probably picked because for other orbits there just was not enough excess capability to have a useful co-manifested payload.

No, that means each "delivery" is constrained by 7.5mt, not the entire DSG.

NASA is pushing quite an aggressive schedule, delivery in 2021 for launch in 2022 for propulsion module.  Habitation module to follow the following year. 

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #15 on: 07/21/2017 06:04 PM »
The other item I noticed was max weight for this co-manifested payload showing there is likely going to this orbit with Orion on a SLS-1B only 7.5mt of excess capability. Which also means that the DSG itself will have to weigh no more than 7.5mt. This orbit was probably picked because for other orbits there just was not enough excess capability to have a useful co-manifested payload.

7.5 mT is the weight of each module. The current plan is for 4 modules.
https://www.nasaspaceflight.com/2017/04/nasa-goals-missions-sls-eyes-multi-step-mars

IMHO A small spacestation containing 4 tiny modules to be lifted by 4 SLS and assembled by 4 Orions appears excessive.

Offline okan170

  • Full Member
  • ****
  • Posts: 1082
  • Los Angeles
  • Liked: 6320
  • Likes Given: 1290
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #16 on: 07/21/2017 06:41 PM »
The other item I noticed was max weight for this co-manifested payload showing there is likely going to this orbit with Orion on a SLS-1B only 7.5mt of excess capability. Which also means that the DSG itself will have to weigh no more than 7.5mt. This orbit was probably picked because for other orbits there just was not enough excess capability to have a useful co-manifested payload.
Yes mass restrictions seem to be popping up and causing development problems, see links below:
http://russianspaceweb.com/imp-ppb.html#2017

http://russianspaceweb.com/imp-lcub.html

Should probably be noted that some of these are due to a less-optimal but safer launch trajectory being used for EM-2, since its the first crew launch.

Online jgoldader

  • Full Member
  • ****
  • Posts: 713
  • Liked: 256
  • Likes Given: 154
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #17 on: 07/21/2017 08:40 PM »
NASA is pushing quite an aggressive schedule, delivery in 2021 for launch in 2022 for propulsion module.  Habitation module to follow the following year. 

Can this really be done by 2021?  This looks like the "hard" part of the Gateway, with the most powerful SEP system ever, no?  Four years to delivery, and no contracts yet?  I could believe a docking node or hab module in 4 years, if there was a lot of money, but the propulsion module seems a lot more ambitious technologically.
Recovering astronomer

Offline okan170

  • Full Member
  • ****
  • Posts: 1082
  • Los Angeles
  • Liked: 6320
  • Likes Given: 1290
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #18 on: 07/21/2017 09:56 PM »
NASA is pushing quite an aggressive schedule, delivery in 2021 for launch in 2022 for propulsion module.  Habitation module to follow the following year. 

Can this really be done by 2021?  This looks like the "hard" part of the Gateway, with the most powerful SEP system ever, no?  Four years to delivery, and no contracts yet?  I could believe a docking node or hab module in 4 years, if there was a lot of money, but the propulsion module seems a lot more ambitious technologically.

Probably helps that its almost literally the latest design of ARM without any of the grabbing equipment and an extra docking port.

Offline ncb1397

  • Full Member
  • ****
  • Posts: 1002
  • Liked: 402
  • Likes Given: 3
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #19 on: 07/21/2017 10:03 PM »
NASA is pushing quite an aggressive schedule, delivery in 2021 for launch in 2022 for propulsion module.  Habitation module to follow the following year. 

Can this really be done by 2021?  This looks like the "hard" part of the Gateway, with the most powerful SEP system ever, no?  Four years to delivery, and no contracts yet?  I could believe a docking node or hab module in 4 years, if there was a lot of money, but the propulsion module seems a lot more ambitious technologically.

Probably helps that its almost literally the latest design of ARM without any of the grabbing equipment and an extra docking port.

ARM had a docking port for Orion. PPE would just need the one. Right?


Offline okan170

  • Full Member
  • ****
  • Posts: 1082
  • Los Angeles
  • Liked: 6320
  • Likes Given: 1290
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #20 on: 07/21/2017 10:22 PM »
ARM had a docking port for Orion. PPE would just need the one. Right?

The RFP specifies 2 IDSS-compatible interfaces.  The single ARM one was on the "rear" of the spacecraft (from which the SEP engines are offset) and the new one is in the "nose" where the grabber mechanism would've been. 

Offline Propylox

  • Member
  • Posts: 81
  • Colorado
  • Liked: 6
  • Likes Given: 7
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #21 on: 07/22/2017 01:14 AM »
"Near rectilinear halo orbit" is a non-starter. [...] Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.
Is part of it about wanting a big SEP project in a post-ARM world?  Back-solving from the tech they want to fund?
I'm all for "a big SEP" to transport propellant and infrastructure from (commercial) LEO to (DSG) LLO, but nothing about ARM or this DSG RFI addresses that. I define "big" as 800 to 1,000 kW and capable of +25mT in a 6mo roundtrip. The 12kW HETs won't cut it so don't need testing.

What use is DSG at LLO when no one can visit it. Orion could make it to LLO but it would be oneway trip.
The problem is Orion cannot enter and then exit LLO, so no infrastructure using Orion will be built or moved there.
The leftover ATV and Shuttle OME re-purposed as Orion's temporary Service Module contains 9mT propellant for ~ 1,350 m/s delta-v and isn't capable of LLO missions. But increasing propellant by 6mT to a wetmass of 32mT is ~ 2,000 m/s delta-v. This is enough for LLO and return with ample capabilities and margin.

I thought low lunar orbits (LLO) were unstable, requiring between 0-400 m/s of station keeping.

Putting the DSG in LLO would make lunar landing much easier.
Some are highly unstable, others entirely stable due to the Moon's mass/gravity distribution.

There's no point building a rocket and capsule to go to the Moon if we're not landing and the lower the staging orbit, the less propellant is required per trip. But this assumes the propellant is delivered via SEP, not chemically like Orion.

7.5 mT is the weight of each module. The current plan is for 4 modules.
https://www.nasaspaceflight.com/2017/04/nasa-goals-missions-sls-eyes-multi-step-mars

IMHO A small spacestation containing 4 tiny modules to be lifted by 4 SLS and assembled by 4 Orions appears excessive.
Especially when a functional 42-day docking berth can be placed in LLO with a single TSTO cargo launch. Just not the design and orbit listed in the RFI - because NASA, of course.
« Last Edit: 07/22/2017 11:53 PM by Propylox »

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #22 on: 07/22/2017 01:50 AM »
4 modules comes to about 30mt total delivered with 4 SLS/Orion flights. It is interesting to note that a single SLS/Cargo flight could deliver all 4 modules at once. If the 5th SLS flight will be in 2026 (New RS25E's) and the 6th flight in 2028. That makes the DSG fully functional for use NET 2026 when the first habitat module is delivered. 2 SLS flights prior to the DSG habitat delivery (5th SLS flight) is the Europa Clipper flights (SLS #2/3 and #4). If the EC Lander is delayed then the Habitat could be 2 years earlier but would also require a human rated habitat to be completed/developed in 6 years from now. That is really pushing it since the habitat has yet to even be on contract, not even close to a PDR point (probably at least 3 years away 2020) , CDR a year latter (2021) then 3 years to build and certify the habitat (2024) then a year later launch (2025). So SLS flt #4 could be as late as 2025 if EC#2 (Lander) development is delayed into second half of 2020's.

But to get all 4 DSG modules in orbit could be as late as 2030.

But this PPE design is useful for other uses than just the DSG. So it may have a life of it's own regardless of SLS/Orion or even DSG.

Offline Propylox

  • Member
  • Posts: 81
  • Colorado
  • Liked: 6
  • Likes Given: 7
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #23 on: 07/22/2017 02:05 AM »
... But this PPE design is useful for other uses than just the DSG.
So it may have a life of it's own regardless of SLS/Orion or even DSG.
I'd counter this PPE may have a thousand uses, but DSG ain't one.
Manned habitation, docking attempts, or any sort of mission won't be occurring from that orbit. Meaning DSG will be somewhere else while PPE floats about. If/when DSG is planned for a useful orbit, the electric propulsion system this PPE sports won't be necessary or wanted. Meaning this PPE won't be part of DSG, though that's how NASA is selling it. You buying?

Offline ncb1397

  • Full Member
  • ****
  • Posts: 1002
  • Liked: 402
  • Likes Given: 3
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #24 on: 07/22/2017 02:52 AM »
If the EC Lander is delayed then the Habitat could be 2 years earlier but would also require a human rated habitat to be completed/developed in 6 years from now. That is really pushing it since the habitat has yet to even be on contract, not even close to a PDR point (probably at least 3 years away 2020) , CDR a year latter (2021) then 3 years to build and certify the habitat (2024) then a year later launch (2025). So SLS flt #4 could be as late as 2025 if EC#2 (Lander) development is delayed into second half of 2020's.

Boeing was selected as ISS prime contractor in 1993 and Unity was launched 5 and a half years later in December 1998. If they select one or two of the NextStep Hab partners(Boeing, SNC, Bigelow, Lockheed Martin or Orbital) in 2018, they have a reasonable shot of launching it is 2024 which would be 6 years later. Probably helps the schedule that we have basically been through this rodeo before.

Offline okan170

  • Full Member
  • ****
  • Posts: 1082
  • Los Angeles
  • Liked: 6320
  • Likes Given: 1290
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #25 on: 07/22/2017 02:58 AM »
... But this PPE design is useful for other uses than just the DSG.
So it may have a life of it's own regardless of SLS/Orion or even DSG.
I'd counter this PPE may have a thousand uses, but DSG ain't one.
Manned habitation, docking attempts, or any sort of mission won't be occurring from that orbit. Meaning DSG will be somewhere else while PPE floats about. If/when DSG is planned for a useful orbit, the electric propulsion system this PPE sports won't be necessary or wanted. Meaning this PPE won't be part of DSG, though that's how NASA is selling it. You buying?

Calm down, NASA will still be around for you to hate for some time.   ::)  Also I'm not sure "Any sort of mission won't be occurring from that orbit" just because you feel that way and dislike the idea.  There are a few missions planned so far, theres no physical reason why they won't happen.
« Last Edit: 07/22/2017 06:08 AM by okan170 »

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #26 on: 07/22/2017 08:46 PM »
... But this PPE design is useful for other uses than just the DSG.
So it may have a life of it's own regardless of SLS/Orion or even DSG.
I'd counter this PPE may have a thousand uses, but DSG ain't one.
Manned habitation, docking attempts, or any sort of mission won't be occurring from that orbit. Meaning DSG will be somewhere else while PPE floats about. If/when DSG is planned for a useful orbit, the electric propulsion system this PPE sports won't be necessary or wanted. Meaning this PPE won't be part of DSG, though that's how NASA is selling it. You buying?

Supplying a 30-40 tonne spacestation with 400 m/s of station keeping per year is going to require a significant amount of thrusting. A propellant depot and lander will significantly increase the mass.

Turning a second PPE into an Isp 4,190 space tug is fairly easy. Low thrust LEO to LLO is a delta-v of 8.0 km/s one way.

A Masten and ULA Xeus reusable lander should be able to land Moon base modules, rovers and with a capsule people.

Offline JazzFan

  • Full Member
  • **
  • Posts: 206
  • Florida
  • Liked: 27
  • Likes Given: 12
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #27 on: 07/22/2017 11:19 PM »
Will the Power/Propulsion module be a clean sheet design or use an existing bus or propulsion module as a foundation to build upon?

Offline Archibald

  • Senior Member
  • *****
  • Posts: 2551
  • Liked: 447
  • Likes Given: 1039
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #28 on: 07/23/2017 08:04 AM »
Don't feed the troll...
... that ackward moment when you realize that Jeff Bezos personal fortune is far above NASA annual budget... 115 billion to 18 billion...

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #29 on: 07/23/2017 03:20 PM »
Literally this PPE is a "DEEP SPACE TUG". It has advanced docking adapters for in-space attachment of any "payload" and sufficient DV to push some significant sized items around. As I said before and probably is the reason NASA wants to build it in the first place is that this PPE has a multitude of uses outside of just the SLS/Orion/DSG program. Also with its fore and aft docking it can be stacked with multiple PPE to create a very large outer planetary DV delivery system. Think of mating this PPE to a dedicated Europa Lander. This then makes the EC Lander a simpler design such that the power and propulsion is designed leaving only the communication and experiment packages. Also if this vehicle was to also have a significant communication relay capability then the payload no longer need that either. This module then becomes if used to send stuff to Mars a orbital communication relay with its very high power solar arrays capable of multiple high data rate channels for multiple ground assets and links to Earth. 24KW is 2X the power used on HTS comm sats.

Added:
A question then is the intent to make this PPE have a diameter when stowed such that it could fit in a 5m fairing? If so then it definitely has a future for use in the planetary programs. Much less any HSF programs that eventually get approved regardless of SHLV that is used in that program.

I like this vehicle. It shows some forethought into a "LEGO" in-space methodology. Many have thought that the customized each vehicle method has always been the wrong way to go for shortening the development time and development costs. A more "LEGO" approach where stuff is just docked together on the ground at launch or even in-space docking using smaller LV's gives a large set of options for programs to choose quicker and lest costly development paths. This will also help the DSG in that it offloads much of the design problems of the DSG into logical "LEGO" pieces that can be individually tested and improved/replaced if needed.
« Last Edit: 07/23/2017 03:33 PM by oldAtlas_Eguy »

Offline Endeavour_01

  • Full Member
  • ****
  • Posts: 533
  • Physics Professor in SC, USA
  • Liked: 456
  • Likes Given: 429
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #30 on: 07/23/2017 06:25 PM »
"Near rectilinear halo orbit" is a non-starter. If you'd like to know more about the impossibility of station keeping, manned habitation and severe constraints on every mission plan it creates, NASA has plenty of papers - oddly pointing this out and concluding we should do it anyways. Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Cislunar Near Rectilinear Halo Orbit for Human Space Exploration - Sept 2016
https://ntrs.nasa.gov/search.jsp?R=20160003078

I was only able to read the abstract of that paper but from what I read it doesn't seem that the authors are declaring NRO orbits impossible or worthless. They are pointing out that NROs have never been used for human exploration and that different orbital models will be required. It's a challenge but not an impossible one.

Attached is another paper that I ran across in NSF a while ago that is quite positive on the usage of NROs for human exploration.

I cheer for both NASA and commercial space. For SLS, Orion, Falcon 9, Falcon Heavy, Dragon, Starliner, Cygnus and all the rest!
I was blessed to see the launch of Space Shuttle Endeavour on STS-99. The launch was beyond amazing. My 8-year old mind was blown. I remember the noise and seeing the exhaust pour out of the shuttle as it lifted off. I remember staring and watching it soar while it was visible in the clear blue sky. It was one of the greatest moments of my life and I will never forget it.

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #31 on: 07/23/2017 07:33 PM »
"Near rectilinear halo orbit" is a non-starter. If you'd like to know more about the impossibility of station keeping, manned habitation and severe constraints on every mission plan it creates, NASA has plenty of papers - oddly pointing this out and concluding we should do it anyways. Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Cislunar Near Rectilinear Halo Orbit for Human Space Exploration - Sept 2016
https://ntrs.nasa.gov/search.jsp?R=20160003078

I was only able to read the abstract of that paper but from what I read it doesn't seem that the authors are declaring NRO orbits impossible or worthless. They are pointing out that NROs have never been used for human exploration and that different orbital models will be required. It's a challenge but not an impossible one.

Attached is another paper that I ran across in NSF a while ago that is quite positive on the usage of NROs for human exploration.
The one distinct advantage of L2 is that launch windows to that destination are not overly complex. But NRO's require specific timing of the object in the NRO with the Earth's rotation which could be highly restrictive. But for SLS that is unlikly to launch more than once a year that is not really a concern. But for an active continuously manned DSG where commercial services are resupplying and possibly even delivering crews such orbits would represent significant launch scheduling conflicts and other possible lengthy delays when a window is missed.

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #32 on: 07/24/2017 02:41 AM »
Literally this PPE is a "DEEP SPACE TUG". It has advanced docking adapters for in-space attachment of any "payload" and sufficient DV to push some significant sized items around. As I said before and probably is the reason NASA wants to build it in the first place is that this PPE has a multitude of uses outside of just the SLS/Orion/DSG program. Also with its fore and aft docking it can be stacked with multiple PPE to create a very large outer planetary DV delivery system. Think of mating this PPE to a dedicated Europa Lander. This then makes the EC Lander a simpler design such that the power and propulsion is designed leaving only the communication and experiment packages. Also if this vehicle was to also have a significant communication relay capability then the payload no longer need that either. This module then becomes if used to send stuff to Mars a orbital communication relay with its very high power solar arrays capable of multiple high data rate channels for multiple ground assets and links to Earth. 24KW is 2X the power used on HTS comm sats.

Added:
A question then is the intent to make this PPE have a diameter when stowed such that it could fit in a 5m fairing? If so then it definitely has a future for use in the planetary programs. Much less any HSF programs that eventually get approved regardless of SHLV that is used in that program.

I like this vehicle. It shows some forethought into a "LEGO" in-space methodology. Many have thought that the customized each vehicle method has always been the wrong way to go for shortening the development time and development costs. A more "LEGO" approach where stuff is just docked together on the ground at launch or even in-space docking using smaller LV's gives a large set of options for programs to choose quicker and lest costly development paths. This will also help the DSG in that it offloads much of the design problems of the DSG into logical "LEGO" pieces that can be individually tested and improved/replaced if needed.

I cannot see any mention of the fairing size in the RFI. So if an aerospace firm can design the PPE to fit into a 5m fairing they may get NASA to pay for development of their SEP tug.

Offline ncb1397

  • Full Member
  • ****
  • Posts: 1002
  • Liked: 402
  • Likes Given: 3
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #33 on: 07/24/2017 05:43 PM »
"Near rectilinear halo orbit" is a non-starter. If you'd like to know more about the impossibility of station keeping, manned habitation and severe constraints on every mission plan it creates, NASA has plenty of papers - oddly pointing this out and concluding we should do it anyways. Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Cislunar Near Rectilinear Halo Orbit for Human Space Exploration - Sept 2016
https://ntrs.nasa.gov/search.jsp?R=20160003078

I was only able to read the abstract of that paper but from what I read it doesn't seem that the authors are declaring NRO orbits impossible or worthless. They are pointing out that NROs have never been used for human exploration and that different orbital models will be required. It's a challenge but not an impossible one.

Attached is another paper that I ran across in NSF a while ago that is quite positive on the usage of NROs for human exploration.
The one distinct advantage of L2 is that launch windows to that destination are not overly complex. But NRO's require specific timing of the object in the NRO with the Earth's rotation which could be highly restrictive. But for SLS that is unlikly to launch more than once a year that is not really a concern. But for an active continuously manned DSG where commercial services are resupplying and possibly even delivering crews such orbits would represent significant launch scheduling conflicts and other possible lengthy delays when a window is missed.

Not true...

Quote
We found that in order to minimize Orion propellent usage, the optimizer was adjusting the outbound
trip times to keep the arrival in and departure from the NRHO near the favorable regions of
the NRHO for those maneuvers. In terms of Orion propellant used, the rendezvous missions would
approach the performance of the free-phase missions once per NRHO period. At these points near
the phase match, there would typically be from 3 to 5 consecutive feasible rendezvous mission
opportunities, with the best approaching the performance of the free-phase cases (see Figure 13).
For the short stay missions examined, this means that there would be multiple sets of launch opportunities
each month
, with each set spanning 3 to 5 consecutive days. The results also indicate
that, at least broadly, the previous free-phase results can be used to gain insight into the general
performance situation for fixed-phase trajectories.
https://ntrs.nasa.gov/search.jsp?R=20170001352

These are launch opportunities with Orion towing a 10 ton module to rendezvous with another object already in that orbit.
« Last Edit: 07/24/2017 05:51 PM by ncb1397 »

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32378
  • Cape Canaveral Spaceport
  • Liked: 11065
  • Likes Given: 329
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #34 on: 07/24/2017 06:05 PM »

I cannot see any mention of the fairing size in the RFI. So if an aerospace firm can design the PPE to fit into a 5m fairing they may get NASA to pay for development of their SEP tug.

NASA is paying for the development of a SEP tug, that is what PPE is.

Offline DreamyPickle

  • Full Member
  • *
  • Posts: 188
  • Home
  • Liked: 80
  • Likes Given: 18
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #35 on: 07/24/2017 11:32 PM »
Isn't it a rather *small* SEP tug at 7500 kg? Launching it together with an Orion puts some severe limitations on it.

Also, isn't the whole point of a SEP tug to move payloads around? I'd expect a real tug to continuously carry payloads from LEO, perhaps synchronized with cargo flights. But it seems the plan is for this to sit in the same orbit for years.

I'd rather describe this as a small space-station core module, providing power and station-keeping.

Offline okan170

  • Full Member
  • ****
  • Posts: 1082
  • Los Angeles
  • Liked: 6320
  • Likes Given: 1290
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #36 on: 07/24/2017 11:36 PM »
Isn't it a rather *small* SEP tug at 7500 kg? Launching it together with an Orion puts some severe limitations on it.

Also, isn't the whole point of a SEP tug to move payloads around? I'd expect a real tug to continuously carry payloads from LEO, perhaps synchronized with cargo flights. But it seems the plan is for this to sit in the same orbit for years.

I'd rather describe this as a small space-station core module, providing power and station-keeping.

It has to be able to move between different orbits to support different objectives.

Offline Propylox

  • Member
  • Posts: 81
  • Colorado
  • Liked: 6
  • Likes Given: 7
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #37 on: 07/25/2017 01:28 AM »
Quote
We found that in order to minimize Orion propellent usage, the optimizer was adjusting the outbound
trip times to keep the arrival in and departure from the NRHO near the favorable regions of
the NRHO for those maneuvers. In terms of Orion propellant used, the rendezvous missions would
approach the performance of the free-phase missions once per NRHO period.
https://ntrs.nasa.gov/search.jsp?R=20170001352
These are launch opportunities with Orion towing a 10 ton module to rendezvous with another object already in that orbit.
Fantastic. This implies there are a few opportunities each month to descend to the surface or to schedule a return from the surface. If there's a surface emergency, they'll just have to die waiting for orbital alignment. If an emergency arises while in orbit, can we safely say only half the orbit allows direct to Earth-return. The other half is also death? Great plan.

Offline DreamyPickle

  • Full Member
  • *
  • Posts: 188
  • Home
  • Liked: 80
  • Likes Given: 18
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #38 on: 07/25/2017 01:47 AM »
Perhaps I was too quick to dismiss this. But I'm having trouble evaluating how well this would work if used as an actual SEP tug between LEO and NRHO. I can't even find good numbers for the required delta-V to reach NRHO using low thrust maneuvers, is ~8 km/s from wikipedia OK?

Assuming a 500kg adaptor, 5000 kg dry mass and 9000 ISP you need to reserve ~500 kg fuel for a trip back and the remaining ~1500kg is enough to send ~10tons to the moon. This is from some quick excel math, hope I'm at least in the right ballpark.

Such a payload is on the low end of EELV-to-LEO capabilities but that's not necessarily bad if you want cheap cargo. But ideally you would want a SEP tug capable of transferring payloads as large as you can place in LEO, right?

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #39 on: 07/25/2017 04:06 AM »

I cannot see any mention of the fairing size in the RFI. So if an aerospace firm can design the PPE to fit into a 5m fairing they may get NASA to pay for development of their SEP tug.

NASA is paying for the development of a SEP tug, that is what PPE is.

Correct. I have met salesmen and company directors who think because it is called a PPE that the machine cannot also be a SEP tug. They would expect the second machine to be designed from scratch.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32378
  • Cape Canaveral Spaceport
  • Liked: 11065
  • Likes Given: 329
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #40 on: 07/25/2017 01:39 PM »

Correct. I have met salesmen and company directors who think because it is called a PPE that the machine cannot also be a SEP tug. They would expect the second machine to be designed from scratch.

Any salesmen and company directors who think like that are not capable of managing or building such a project; and would be quickly dropped from competing on such a project.

And actually in the real world, there are no such salesmen and company directors who think like that. 

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #41 on: 07/25/2017 04:42 PM »
Quote
We found that in order to minimize Orion propellent usage, the optimizer was adjusting the outbound
trip times to keep the arrival in and departure from the NRHO near the favorable regions of
the NRHO for those maneuvers. In terms of Orion propellant used, the rendezvous missions would
approach the performance of the free-phase missions once per NRHO period.
https://ntrs.nasa.gov/search.jsp?R=20170001352
These are launch opportunities with Orion towing a 10 ton module to rendezvous with another object already in that orbit.
Fantastic. This implies there are a few opportunities each month to descend to the surface or to schedule a return from the surface. If there's a surface emergency, they'll just have to die waiting for orbital alignment. If an emergency arises while in orbit, can we safely say only half the orbit allows direct to Earth-return. The other half is also death? Great plan.
Also launch from Earth is implied NRHO having a few opportunities each month vs L2 having an opportunity every day. So for regular opperations NRHO imposes mission planning/scheduling restrictions.

Offline TrevorMonty

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #42 on: 07/25/2017 05:03 PM »
 NRHO gives DSG days over one pole per orbit allowing for direct line of sight into that poles craters for hours if not days.
Ideal for communicating with assets (rovers, landers) in those craters and maybe beaming power using laser.

NRHO is just one of few orbits that DSG can use, between Orion missions it can shift to another.

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #43 on: 07/25/2017 06:51 PM »
NRHO gives DSG days over one pole per orbit allowing for direct line of sight into that poles craters for hours if not days.
Ideal for communicating with assets (rovers, landers) in those craters and maybe beaming power using laser.

NRHO is just one of few orbits that DSG can use, between Orion missions it can shift to another.
I understand that NHRO is easy to use to get to other Lunar orbits. It is practically a transfer orbit between HLO and LLO with very small DV to change orbits. But as a more permanent orbit location it has many disadvantages. As discussed earlier it is the fact that it takes less DV from Earth to reach a NHRO than L2 is the probably the main reason it is being picked because of SLS/Orion shortfalls when carrying a co-payload. Also NASA has yet to figure out exact how the DSG will ultimately be used. Use also specifies the orbit. By picking NHRO initially the usage determination can wait until the DSG is actually orbiting around the Moon. A delayed Mars program means that Lunar surface becomes a higher priority and with LLO being more desirable, although the same could be said for L2 but that depends on the lander hardware designs used. An accelerated Mars program would make L2 a desirable orbit.

Offline Propylox

  • Member
  • Posts: 81
  • Colorado
  • Liked: 6
  • Likes Given: 7
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #44 on: 07/26/2017 12:24 AM »
1) But I'm having trouble evaluating how well this would work if used as an actual SEP tug between LEO and NRHO. Assuming 9000 ISP (snip)
2) But ideally you would want a SEP tug capable of transferring payloads as large as you can place in LEO, right?
Re1) The PPE uses HETs while 9,ooo isp assumes either HiPEP or VASIMR. Ion thruster architectures vary how power, fuel rate and isp are interchangeable. Here's a quick overview that I encourage others members to expand upon and/or correct;

 - HET: Invented and perfected by the Soviets, these run at constant wattage. Volts vs Amps directly affects isp as fuel rate is modified, affecting thrust. For example a 24kW thruster could run at 800V x 30A = 2800s isp with high kg/s and thrust. It could switch to 1600V x 15A = 6200s isp, but with reduced kg/s and thrust. It alternates isp and voltage for thrust and amperage at the same power level.

 - VASIMR: NASA designed and privately perfected, it's meant for constant wattage and radio frequency. With a steady electric state, fuel rate determines isp and thrust (N = g * isp * kg/s). As kg/s increases, isp decreases with the highest thrust (efficiency) achieved around 3000-6000s or 10,000s with hydrogen (IIRC - 30,000s with hydrogen is possible at low thrust).

 - HiPEP: NASA designed and put on ice ten yrs ago, wattage is proportional to fuel rate, isp and thrust. For example 9.7kW x 4.0 mg/s = 5970s and 240mN thrust while cranked to 39.9kW x 7.0 mg/s = 9620s and 670mN thrust. It's not entirely linear, as efficiency changes, but generally.

Re2) Ideally the SEP tug would be sized to the LV providing its payload. If a 37-38mT FH is used, the tug would deliver 29-30mT to LLO with 8mT fuel. If a 25mT AresI is used, the tug should deliver 19-20mT to LLO with 5-6mt fuel. Both assume an average isp around 4500s.

Additions/Corrections?
« Last Edit: 07/26/2017 12:38 AM by Propylox »

Offline TrevorMonty

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #45 on: 07/26/2017 01:21 AM »


A delayed Mars program means that Lunar surface becomes a higher priority and with LLO being more desirable, although the same could be said for L2 but that depends on the lander hardware designs used. An accelerated Mars program would make L2 a desirable orbit.

Orion is limiting factor on LLO.

Online docmordrid

  • Senior Member
  • *****
  • Posts: 4926
  • Michigan
  • Liked: 2038
  • Likes Given: 1
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #46 on: 07/26/2017 02:09 AM »
Add: MSNW's Electrodeless Lorentz Force Thruster (ELF), which was funded under NextSTEP.

Patent
http://www.google.com/patents/US20120031070
« Last Edit: 07/26/2017 02:19 AM by docmordrid »
DM

Offline Propylox

  • Member
  • Posts: 81
  • Colorado
  • Liked: 6
  • Likes Given: 7
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #47 on: 07/27/2017 01:00 AM »
--- continued on ion architecture ---

Unfortunately there's only assumptions and hurdles with high-power applications for all three ion options mentioned. The PPE is a puny design, both in power levels and capabilities, that doesn't address any current and future needs or advance technology that is needed. And that orbit.

 - HET: Material science currently limits cathodes to around 30-50 amps without rapid degradation. It's why I suggested a variable voltage to use high amps/thrust deep in gravity wells and plane changes, then switch to high voltage/isp for spiraling. This preserves the engine, increases efficiency and transit time.
Additionally a grid, or cluster of multiple HETs arc across each other, rapidly destroying one at a time. PPE uses broadly-spaced, low power HETs to avoid this while tests have used external magnetic containment poles to isolate each HET. Packing 20-30 HETS of 30-50kW together for a viable SEP tug seems highly problematic.

 - VASIMR: Weight and reliability are the major questions. This architecture requires active cooling - possibly regenerative, but that may not be enough. If not there's additional system weight and reliability questions.
VASIMR's also never done long-duration testing like was planned aboard ISS to prove reliability. This may be a great design, but final operating parameters and design needs to be proven.

 - HiPEP: While ~9,ooos isp and ~40kW was shown, the efficiency study I linked was to test at up to 16kW for a 25kW mission, but never neared that. It focused on temperatures, coupling, efficiency and degradation around 1kW. I'd guess a final design wouldn't be near 9,ooos by increasing kg/s to keep it cool and reliable.
« Last Edit: 07/27/2017 01:05 AM by Propylox »

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #48 on: 07/27/2017 02:20 PM »
--- continued on ion architecture ---

Unfortunately there's only assumptions and hurdles with high-power applications for all three ion options mentioned. The PPE is a puny design, both in power levels and capabilities, that doesn't address any current and future needs or advance technology that is needed. And that orbit.

 - HET: Material science currently limits cathodes to around 30-50 amps without rapid degradation. It's why I suggested a variable voltage to use high amps/thrust deep in gravity wells and plane changes, then switch to high voltage/isp for spiraling. This preserves the engine, increases efficiency and transit time.
Additionally a grid, or cluster of multiple HETs arc across each other, rapidly destroying one at a time. PPE uses broadly-spaced, low power HETs to avoid this while tests have used external magnetic containment poles to isolate each HET. Packing 20-30 HETS of 30-50kW together for a viable SEP tug seems highly problematic.

 - VASIMR: Weight and reliability are the major questions. This architecture requires active cooling - possibly regenerative, but that may not be enough. If not there's additional system weight and reliability questions.
VASIMR's also never done long-duration testing like was planned aboard ISS to prove reliability. This may be a great design, but final operating parameters and design needs to be proven.

 - HiPEP: While ~9,ooos isp and ~40kW was shown, the efficiency study I linked was to test at up to 16kW for a 25kW mission, but never neared that. It focused on temperatures, coupling, efficiency and degradation around 1kW. I'd guess a final design wouldn't be near 9,ooos by increasing kg/s to keep it cool and reliable.
This sounds like more of a 5 year development program than just a 3 year build program. In a three year build program as being requested (delivery date of 2021 and contract start sometime in FY2018), there is no time to develop technology.

Added:
Some additional technology issues:
1) The solar array should not have any issues. A 12KW array as used on HTS comm sats can be doubled by just doing two of the designed arrays. It then only becomes a problem for mounting, stowage, and deployment of the arrays. Since there are no supper sized antennas to contend with this should be easy.
2) The fore and aft NDS. With a hollow tube >2m distance between them, this could be set up as an air lock. Would also need hatches at both ends. This tube would also be the primary load bearing structure. This also address the main item about the structure and that is that it will be of a new design.
3) Prop tanks, chemical engines, batteries, and avionics would all be "off the shelf" items. In other words they are in production for use on other sats/in-space vehicles.
4) Adding some TDRSS comm system items to the PPE would increase its usefulness for many missions in the future. Such as a comm relay system for far side of the Moon surface missions. But this also adds those pesky large antennas.
« Last Edit: 07/27/2017 02:43 PM by oldAtlas_Eguy »

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #49 on: 07/28/2017 12:24 AM »
{snip}
4) Adding some TDRSS comm system items to the PPE would increase its usefulness for many missions in the future. Such as a comm relay system for far side of the Moon surface missions. But this also adds those pesky large antennas.

Sounds like a surface communications module will be needed. An in space router/base-station that permits several vehicles and habitats on the lunar surface to communicate with each other, the DSG, spacecraft and Earth. This could be delivered by a space tug.

Offline Propylox

  • Member
  • Posts: 81
  • Colorado
  • Liked: 6
  • Likes Given: 7
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #50 on: 07/29/2017 02:26 PM »
This sounds like more of a 5 year development program than just a 3 year build program. In a three year build program as being requested (delivery date of 2021 and contract start sometime in FY2018), there is no time to develop technology.
Very true - but why spend three years building, then launching, then operating something with no use? Wouldn't the time, money and effort be better spent on something you can use and need? As this is an RFI possibilities will be numerous, but none of them - no matter how quick or inexpensive - are actually worth it.
It's not a deal if it's something you don't want. It's actually a waste.
« Last Edit: 07/29/2017 02:29 PM by Propylox »

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32378
  • Cape Canaveral Spaceport
  • Liked: 11065
  • Likes Given: 329
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #51 on: 07/29/2017 03:17 PM »
How do you know it is not wanted?

Online BrightLight

  • Full Member
  • ****
  • Posts: 1341
  • Northern New Mexico
  • Liked: 236
  • Likes Given: 339
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #52 on: 07/31/2017 05:39 PM »
Here is a copy of the RFI itself, replies were due July 28, 2017. The RFi number is RFI: NNH17ZCQ006L

Bold is the technical requirement, and the detailed comments follow in regular text.
Table 1.2.1 PPE Reference Capability Descriptions
1. PPE Lifetime The PPE will have a minimum operational lifetime of 15 years in cis-lunar space.
 The PPE lifetime of 15 years initiates with launch.
2. PPE Power Transfer The PPE will be capable of transferring up to 24kW of electrical power to the external hardware.                      
The 24kW electrical power value represents the maximum amount of power transferred to the external hardware other than the PPE. The 24kW power level would be decreased if the external hardware uses Solar Electric Propulsion (SEP) thrusting. Alternatively, this could limit the available power for SEP thrusting.
3A. PPE Propulsion Capability The PPE will be capable of providing orbit transfers for a stack of TBD mass with a center of gravity of TBD.                                     
The capability of the PPE provides in-space transportation for the external hardware.
3B. PPE Propulsion Capability The PPE will be capable of providing orbit maintenance for a stack of TBD mass with a center of gravity of TBD.                           
The capability of the PPE provides in-space transportation for the external hardware.
4. PPE Xenon Capacity The PPE will have 2,000 kg-class tank Xenon capacity.                 
The capability of the PPE to provide in-space transportation to the external hardware is expressed in terms of Xenon load (proxy for delta-v) rather than a specific number of orbit transfers.
5a. PPE Launch Vehicle The PPE will be compatible with the SLS vehicle co-manifested launch loads on the Exploration Mission -2 (EM-2) flight.                               
The PPE will be subject to the SLS launch mass constraints associated with an Orion co-manifest launch. As EM-2 is planned to be the first crewed SLS launch, co-manifesting PPE with Orion on EM-2 will limit its mass more than if it was on later Exploration Missions. Currently this would constrain the PPE to 7,500 kg total launch mass including the Payload Adapter and any partner provided hardware or systems.
5b. PPE Mass The PPE will not exceed a mass of 7,500 kg including the payload adaptor.                 
It should be understood that there is no explicit or implied commitment for future procurements in this action. 6
6. PPE Attitude Control The PPE will be capable of providing attitude control for external hardware up to (TBD) mass and (TBD) Center of Gravity location.                            
The PPE will provide attitude control using RCS, momentum wheels, SEP thrust vectoring (TBD) for the entire external hardware. The control authority requirements for attitude control will change over time as additional external hardware is added.
7. PPE Interfaces The PPE will be capable of integrating two International Docking System Standard (IDSS) compliant systems.    
 The PPE will be equipped with two IDSS compliant systems, one forward and one aft. These berthing locations will support unpressurized logistics, and robotic arm interfaces and grapple fixtures. The IDSS specification will include interfaces for power, command and data handling and fluids as standard interfaces.
8A. PPE Communication The PPE will be capable of providing X-Band, Ka-Band, S-Band and UHF communications.                                        The PPE will provide communications X-band uplink and downlink and Ka-band downlink with the Ground, and S-band with the external hardware. PPE will support UHF communications with EVA.
8B. PPE Communication The PPE will be capable of accommodating an optical communication demonstration.                                         The PPE will accommodate an optical communication demonstration by providing an attachment to a Passive Base Interface Plate.
9A. PPE Crew Compatibility The PPE will be crew compatible. Crew compatibility compliance will be defined in “Certification Requirements for NASA Deep Space Missions” HEOMD-XX-100X (TBD) document (Note, this document is not available at the release of this RFI).                 
The specific requirements drive aspects of crew safety, hazard controls, and interoperability requirements. The PPE will be compatible with crew EVA but will not require EVA/Extravehicular Robotics repairable equipment.
9B. PPE Crew Compatibility                                  
The PPE will provide a minimum translation path for EVA.
10. PPE Refuelability The PPE will be on-orbit refuelable.                         
The Power and Propulsion Element will have refuel capability incorporated with/near the forward and aft IDSS compliant interfaces for both xenon and hydrazine.
11. PPE Extensibility The PPE will demonstrate an advanced integrated solar electric propulsion system including a 50kW class Solar Electric Propulsion capability that is extensible to future human Mars class missions.                                           
The advanced solar electric propulsion system employs elements that have the solar array power-to-mass ratio, stowed volume efficiency, deployed strength and radiation tolerance, and that have the electric propulsion high-power, specific impulse, and total impulse needed for future Mars missions. This capability also addresses Human Exploration and Operations Exploration Objective P1-06 to demonstrate the operation of long-duration high power solar arrays and SEP transportation of in-space propulsion elements.
12. PPE Lunar Orbit The PPE will insert into a crew-accessible Near Rectilinear Halo Orbit (NRHO) in no longer than 100 days (TBR) after launch.                        
Identification of the NRHO orbit will be needed to scope the mission. (Note, this information is not available at the release of this RFI)

Online BrightLight

  • Full Member
  • ****
  • Posts: 1341
  • Northern New Mexico
  • Liked: 236
  • Likes Given: 339
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #53 on: 08/01/2017 02:44 PM »
HEO Committee power point on Future Exploration Plans by Greg Williams has been posted, including several slides on the PPE

https://www.nasa.gov/sites/default/files/atoms/files/nac_exploration_july_2017_4-2.pdf

Offline titusou

  • Member
  • Posts: 55
  • Tokyo
  • Liked: 81
  • Likes Given: 0
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #54 on: 08/01/2017 04:36 PM »
With 2 IDSS in requirement, plus SEP... how that will be configured?

Assuming SEP on the long-axle, and 1st IDSS on the other end, that will make 2nd IDSS mounted on the side?
How that translated to center-of-mass for station keeping boost? SEP on gimbals?

Attached image is from Orbital ATK's concept video, which have 2 IDSS on 2 end of long-axle. Small thrusters next to one of IDSS, which doesn't seem functional when that IDSS been used.

Or we gonna see Orbital ATK MEV-style HET mounted on extended arm? Which I think is a smart design to somehow adjust the thrust alignment by moving extended arm.


Titus
« Last Edit: 08/01/2017 04:37 PM by titusou »

Offline okan170

  • Full Member
  • ****
  • Posts: 1082
  • Los Angeles
  • Liked: 6320
  • Likes Given: 1290
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #55 on: 08/01/2017 04:56 PM »
With 2 IDSS in requirement, plus SEP... how that will be configured?

Assuming SEP on the long-axle, and 1st IDSS on the other end, that will make 2nd IDSS mounted on the side?
How that translated to center-of-mass for station keeping boost? SEP on gimbals?

Attached image is from Orbital ATK's concept video, which have 2 IDSS on 2 end of long-axle. Small thrusters next to one of IDSS, which doesn't seem functional when that IDSS been used.

Or we gonna see Orbital ATK MEV-style HET mounted on extended arm? Which I think is a smart design to somehow adjust the thrust alignment by moving extended arm.


Titus

Its the last one you described.  Per the renderings from NASA which match the last version of the ARM bus, the SEP thrusters are mounted on moveable arms around the IDSS port (for ARM, Orion was to dock at this port) but most of the gateway seems to be set up to be on the other end of the bus giving it a more traditional-looking configuration. 

I did a quick render here to show the arrangement in the aft compared with the (more exposed) CAD diagrams of the area from NASA.  I do not know if the bus is pass-through (basically a tunnel, like Cygnus DS) or if the IDSS ports are just hard points for moving it around using any compatible vehicle- I'm leaning towards just hard points though simply because I cannot find any information about a tunnel in the design. There is some word of a small science airlock at the "front end" of the bus, but thats from much earlier international discussions and not any NASA documents.
« Last Edit: 08/01/2017 05:55 PM by okan170 »

Offline okan170

  • Full Member
  • ****
  • Posts: 1082
  • Los Angeles
  • Liked: 6320
  • Likes Given: 1290
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #56 on: 08/01/2017 05:28 PM »
BL's copy of the RFI - #7: These berthing locations will support unpressurized logistics ... and #9b: The PPE will provide a minimum translation path for EVA.
I'm assuming that's a tunnel for unpressurized cargo, possibly large enough to pass through or am I misinterpreting "translation path"?

From the terminology, it sounds like they're referring to handrail paths along the outside of the module that allow spacewalkers to access the hard points for logistics and most equipment, or just to cross the module on the way to somewhere else.

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #57 on: 08/02/2017 05:06 AM »

Its the last one you described.  Per the renderings from NASA which match the last version of the ARM bus, the SEP thrusters are mounted on moveable arms around the IDSS port (for ARM, Orion was to dock at this port) but most of the gateway seems to be set up to be on the other end of the bus giving it a more traditional-looking configuration. 

I did a quick render here to show the arrangement in the aft compared with the (more exposed) CAD diagrams of the area from NASA.  I do not know if the bus is pass-through (basically a tunnel, like Cygnus DS) or if the IDSS ports are just hard points for moving it around using any compatible vehicle- I'm leaning towards just hard points though simply because I cannot find any information about a tunnel in the design. There is some word of a small science airlock at the "front end" of the bus, but thats from much earlier international discussions and not any NASA documents.

I assume the main IDSS port is there to allow the PPE to dock to the rest of the DSG and push the DSG. IMHO The chemical thrusters are to allow manoeuvring during docking plus provide roll control and attitude control to the entire spacestation.

The second IDSS may allow the whole DSG to be manoeuvred but its prime role is likely to be the refuelling point for the ion and chemical thrusters. Such connectors are a coming enhancement to the IDSS. If so there will be pipes to the 3 propellant tanks.

Offline Archibald

  • Senior Member
  • *****
  • Posts: 2551
  • Liked: 447
  • Likes Given: 1039
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #58 on: 08/02/2017 01:50 PM »
The great thing with electric propulsion is that the DSG could travel on low-energy trajectories, between GEO, L1, L2, different lunar orbits (DRO, LLO) and finally, Sun-Earth libration points.

Delta-V between these various locations are rather small, 1 km/s or less.

What missions for the DSG ?

- GEO: use a space tug to clean Zombie sats like Galaxy 15.
- EML-1 / EML-2: global communications with lunar surface missions.
- DRO / LLO: supports a reusable lunar lander
- SEL-1 / SEL-2: telescope servicing
... that ackward moment when you realize that Jeff Bezos personal fortune is far above NASA annual budget... 115 billion to 18 billion...

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32378
  • Cape Canaveral Spaceport
  • Liked: 11065
  • Likes Given: 329
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #59 on: 08/02/2017 02:33 PM »
DSG is not going to be used to clean up GEO.

Offline titusou

  • Member
  • Posts: 55
  • Tokyo
  • Liked: 81
  • Likes Given: 0
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #60 on: 08/02/2017 03:34 PM »
I revisit the DSG pdf, and realize in the plan drawing, the only module connected with PPE is Hab (using rear port of Hab). Since Hab has 3 ports in total, front/rear/side, that leave 2 ports available to be used, not blocking station keeping thruster.

And then it's Orion/Logistic/Airlock connected to Hab.

So it's interesting to see why PPE need 2nd IDSS port, and if any of them need to support pressured operation, or both just simply used as structure connecting point.


The wild ideal: assuming you have front of PPE as pressured, and have 2 ports next to each other, front and front-side, then you can basically using PPE as mini pressured node to connect more pressured module to move stuff around.

But that for sure complex everything, and make the net weight challenging to meet. After all we have a 7500kg ceiling for "everything"


Titus

Offline brickmack

  • Full Member
  • ****
  • Posts: 465
  • USA
  • Liked: 174
  • Likes Given: 13
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #61 on: 08/02/2017 03:39 PM »
I did a quick render here to show the arrangement in the aft compared with the (more exposed) CAD diagrams of the area from NASA.

What is the source of that CAD picture?

Offline okan170

  • Full Member
  • ****
  • Posts: 1082
  • Los Angeles
  • Liked: 6320
  • Likes Given: 1290
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #62 on: 08/02/2017 03:56 PM »
I did a quick render here to show the arrangement in the aft compared with the (more exposed) CAD diagrams of the area from NASA.

What is the source of that CAD picture?


"The Ion Propulsion System for the Asteroid Redirect Robotic Mission"  Jul 25, 2016

The Asteroid Redirect Robotic Mission is a Solar Electric Propulsion Technology Demonstration Mission (ARRM) whose main objectives are to develop and demonstrate a high-power solar electric propulsion capability for the Agency and return an asteroidal mass for rendezvous and characterization in a companion human-crewed mission. This high-power solar electric propulsion capability, or an extensible derivative of it, has been identified as a critical part of NASA's future beyond-low-Earth-orbit, human-crewed exploration plans. This presentation presents the conceptual design of the ARRM ion propulsion system, the status of the NASA in-house thruster and power processing development activities, the status of the planned technology maturation for the mission through flight hardware delivery, and the status of the mission formulation and spacecraft acquisition.

https://ntrs.nasa.gov/search.jsp?R=20170002634

PDF is on the page.  This is one of the latest documents I can find of the configuration thats now being used as the DSG Power/Prop Bus in NASA's images.  (I've actually reached out to the authors to see if I can dig up anything more about the module, but haven't heard back yet.)

I revisit the DSG pdf, and realize in the plan drawing, the only module connected with PPE is Hab (using rear port of Hab). Since Hab has 3 ports in total, front/rear/side, that leave 2 ports available to be used, not blocking station keeping thruster.
...

The Habitat module(s) have 4 ports- 2 axial, 2 radial.
« Last Edit: 08/02/2017 05:08 PM by okan170 »

Offline Propylox

  • Member
  • Posts: 81
  • Colorado
  • Liked: 6
  • Likes Given: 7
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #63 on: 08/05/2017 03:34 PM »
HEO Committee power point on Future Exploration Plans by Greg Williams has been posted, including several slides on the PPE https://www.nasa.gov/sites/default/files/atoms/files/nac_exploration_july_2017_4-2.pdf
Is PPE (and ARM) still unfunded in NASA's 2018 budget, suggesting this RFI and assumptions about a DSG in NRHO are merely castoff program dreams? Is it better to wait until a new, actually viable plan is put forth to speculate on DSG and Lunar operations?
« Last Edit: 08/05/2017 03:36 PM by Propylox »

Offline ncb1397

  • Full Member
  • ****
  • Posts: 1002
  • Liked: 402
  • Likes Given: 3
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #64 on: 08/05/2017 04:27 PM »
HEO Committee power point on Future Exploration Plans by Greg Williams has been posted, including several slides on the PPE https://www.nasa.gov/sites/default/files/atoms/files/nac_exploration_july_2017_4-2.pdf
Is PPE (and ARM) still unfunded in NASA's 2018 budget, suggesting this RFI and assumptions about a DSG in NRHO are merely castoff program dreams? Is it better to wait until a new, actually viable plan is put forth to speculate on DSG and Lunar operations?

Not everything that NASA launches has specific funding. Space technology and Advanced Explorations Systems combined have a billion dollar per year budget with NASA having pretty wide latitude with how it is spent(besides the portion of that budget that Congress directs to specific items). It is how they worked on ARM with Congress against it.

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #65 on: 08/06/2017 12:23 AM »
HEO Committee power point on Future Exploration Plans by Greg Williams has been posted, including several slides on the PPE https://www.nasa.gov/sites/default/files/atoms/files/nac_exploration_july_2017_4-2.pdf
Is PPE (and ARM) still unfunded in NASA's 2018 budget, suggesting this RFI and assumptions about a DSG in NRHO are merely castoff program dreams? Is it better to wait until a new, actually viable plan is put forth to speculate on DSG and Lunar operations?

Not everything that NASA launches has specific funding. Space technology and Advanced Explorations Systems combined have a billion dollar per year budget with NASA having pretty wide latitude with how it is spent(besides the portion of that budget that Congress directs to specific items). It is how they worked on ARM with Congress against it.

Currently DSG development is being paid for using the NextSTEP budget
https://www.nasa.gov/nextstep

The Deep Space Power and Propulsion Element (PPE) has just reached the Request for Information (RFI) i.e. no money yet stage.
https://www.nasa.gov/feature/nasa-power-propulsion-rfi
« Last Edit: 08/06/2017 12:24 AM by A_M_Swallow »

Offline Ben the Space Brit

  • Senior Member
  • *****
  • Posts: 7126
  • A spaceflight fan
  • London, UK
  • Liked: 646
  • Likes Given: 759
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #66 on: 08/07/2017 10:39 AM »
Purely FWIW, does the 2026 configuration of DSG remind anyone else of Skylab? Maybe they can call it 'Moonlab'? (Yes, I know, I know, my Steven Baxter fanboy is showing again!)
"Oops! I left the silly thing in reverse!" - Duck Dodgers

~*~*~*~

The Space Shuttle Program - 1981-2011

The time for words has passed; The time has come to put up or shut up!
DON'T PROPAGANDISE, FLY!!!

Offline dkovacic

  • Full Member
  • *
  • Posts: 196
  • Liked: 42
  • Likes Given: 25
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #67 on: 08/11/2017 10:12 AM »
Could PPE also be used as ISS booster? Since it will have IDSS it can dock. If I calculated it right, it could provide up to 30m/s dV per year over five years without refueling.


Offline Archibald

  • Senior Member
  • *****
  • Posts: 2551
  • Liked: 447
  • Likes Given: 1039
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #68 on: 08/11/2017 11:38 AM »
Purely FWIW, does the 2026 configuration of DSG remind anyone else of Skylab? Maybe they can call it 'Moonlab'? (Yes, I know, I know, my Steven Baxter fanboy is showing again!)

you nailed it perfectly. Surely, it looks like Skylab silhouette.
... that ackward moment when you realize that Jeff Bezos personal fortune is far above NASA annual budget... 115 billion to 18 billion...

Offline AnalogMan

  • Member
  • Senior Member
  • *****
  • Posts: 3005
  • Cambridge, UK
  • Liked: 770
  • Likes Given: 23
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #69 on: 08/17/2017 10:31 PM »
Draft version of Level 3 & 4 Requirements for the Power and Propulsion Element (PPE) were published yesterday.  Copy attached.

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #70 on: 08/18/2017 06:50 PM »
Thanks for the document.

There are a few items that requires mention. This PPE will be the primary communications device for the DSG as long as it is attached to the other DSG elements. It also provides the battery power during solar array eclipses. So the other DSG elements would have very minimal batteries and communications. Unfortunately the weights and other capabilities for orbit maneuvers and RCS are TBD.

There is no mention of a air lock or capability of moving through the two docking ports by personnel. So this document does not require that these ports be anything more than a place holder for other elements that provide for power, communications, and prop transfer but nothing more than a structural attach point. No crew egress. That makes a small problem with the Orion in that it cannot dock at the PPE and still do EVA or crew swap. This makes the supply procedures more complex for the DSG. Requiring the supply VV to dock at a crew access port first to be unloaded then undock and move to the PPE to transfer propellant. This would have to be done unless the other DSG elements all have additional piping and valves to be able to transfer prop through these other elements from the VV to the PPE.

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #71 on: 08/19/2017 09:36 PM »
Thanks for the document.

There are a few items that requires mention. This PPE will be the primary communications device for the DSG as long as it is attached to the other DSG elements. It also provides the battery power during solar array eclipses. So the other DSG elements would have very minimal batteries and communications. Unfortunately the weights and other capabilities for orbit maneuvers and RCS are TBD.

There is no mention of a air lock or capability of moving through the two docking ports by personnel. So this document does not require that these ports be anything more than a place holder for other elements that provide for power, communications, and prop transfer but nothing more than a structural attach point. No crew egress. That makes a small problem with the Orion in that it cannot dock at the PPE and still do EVA or crew swap. This makes the supply procedures more complex for the DSG. Requiring the supply VV to dock at a crew access port first to be unloaded then undock and move to the PPE to transfer propellant. This would have to be done unless the other DSG elements all have additional piping and valves to be able to transfer prop through these other elements from the VV to the PPE.

I suspect that the DSG will be refuelled by unmanned cargo vehicles. Since the PPE's fuel tank can only take 2000 kg of propellant the Commercial Resupply Service DSG (CRS-DSG) can be performed in several ways. Most cheaper than Orion on SLS.

Offline tdperk

  • Full Member
  • **
  • Posts: 286
  • Liked: 94
  • Likes Given: 38
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #72 on: 08/20/2017 03:25 PM »

...

( Is it counter to politeness here to use ellipsis to show text has been removed? - tdperk)

I suspect that the DSG will be refuelled by unmanned cargo vehicles. Since the PPE's fuel tank can only take 2000 kg of propellant the Commercial Resupply Service DSG (CRS-DSG) can be performed in several ways. Most cheaper than Orion on SLS.

If NASA for some reason wants to continue avoiding necessary technology development, then instead of mastering bulk liquid fuel transfer in weightlessness, a propulsion module which docks to a DSG or other structure to maneuver it and undocks to permit a fresh one to attach should be developed.  That propulsion module should include or be compatible with a return capability for refurbishment.

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #73 on: 08/20/2017 09:21 PM »

...

( Is it counter to politeness here to use ellipsis to show text has been removed? - tdperk)

I suspect that the DSG will be refuelled by unmanned cargo vehicles. Since the PPE's fuel tank can only take 2000 kg of propellant the Commercial Resupply Service DSG (CRS-DSG) can be performed in several ways. Most cheaper than Orion on SLS.

If NASA for some reason wants to continue avoiding necessary technology development, then instead of mastering bulk liquid fuel transfer in weightlessness, a propulsion module which docks to a DSG or other structure to maneuver it and undocks to permit a fresh one to attach should be developed.  That propulsion module should include or be compatible with a return capability for refurbishment.
Too complex, and easier to just ship 1-2mt of prop up with a regular commercial re-supply vehicle.

Offline tdperk

  • Full Member
  • **
  • Posts: 286
  • Liked: 94
  • Likes Given: 38
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #74 on: 08/21/2017 12:29 AM »

...

( Is it counter to politeness here to use ellipsis to show text has been removed? - tdperk)

I suspect that the DSG will be refuelled by unmanned cargo vehicles. Since the PPE's fuel tank can only take 2000 kg of propellant the Commercial Resupply Service DSG (CRS-DSG) can be performed in several ways. Most cheaper than Orion on SLS.

If NASA for some reason wants to continue avoiding necessary technology development, then instead of mastering bulk liquid fuel transfer in weightlessness, a propulsion module which docks to a DSG or other structure to maneuver it and undocks to permit a fresh one to attach should be developed.  That propulsion module should include or be compatible with a return capability for refurbishment.
Too complex, and easier to just ship 1-2mt of prop up with a regular commercial re-supply vehicle.

After the technology of bulk weightless liquid transfer is established it would be more complex, maybe.

And I have had people tell me the reason SpaceX cannot possibly succeed with the ITS/BFT is that no one knows how to transfer liquids in bulk--so that's a showstopper.  That we cannot count on that task being handled. :P
« Last Edit: 08/21/2017 12:32 AM by tdperk »

Offline envy887

  • Senior Member
  • *****
  • Posts: 4502
  • Liked: 2439
  • Likes Given: 1367
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #75 on: 08/22/2017 02:30 PM »
After the technology of bulk weightless liquid transfer is established it would be more complex, maybe.

And I have had people tell me the reason SpaceX cannot possibly succeed with the ITS/BFT is that no one knows how to transfer liquids in bulk--so that's a showstopper.  That we cannot count on that task being handled. :P

The technology is well established. They already do bulk propellant transfer for ISS.

Online oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 3459
  • Florida
  • Liked: 1864
  • Likes Given: 223
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #76 on: 08/22/2017 03:18 PM »
After the technology of bulk weightless liquid transfer is established it would be more complex, maybe.

And I have had people tell me the reason SpaceX cannot possibly succeed with the ITS/BFT is that no one knows how to transfer liquids in bulk--so that's a showstopper.  That we cannot count on that task being handled. :P

The technology is well established. They already do bulk propellant transfer for ISS.
Note: This technology that is well established is for store-able prop and gaseous prop like argon. But that is what the PPE is dealing with. These two prop types do not require the acceleration settling to perform transfers. They are simplistic and is mainly a problem of valves, piping and connect/disconnects at the docking adapter. It is the cryo prop transfer that is not well established.

Online BrightLight

  • Full Member
  • ****
  • Posts: 1341
  • Northern New Mexico
  • Liked: 236
  • Likes Given: 339
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #77 on: 11/30/2017 03:07 PM »
Update on PP&E work from industry contracts.
From:
https://www.nasa.gov/directorates/heo/nac-heoc
https://www.nasa.gov/sites/default/files/atoms/files/20171130-nac-heoc-ppe_final2.pdf

The 45 day studies are due in January of 2018.

Also shown is an updated DSG from Lockheed Martin with a "newer" version of the PP&E module.
« Last Edit: 11/30/2017 03:21 PM by BrightLight »

Offline JacobLutz7

  • Member
  • Posts: 1
  • United States
  • Liked: 0
  • Likes Given: 0
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #78 on: 01/20/2018 06:23 PM »
"Near rectilinear halo orbit" is a non-starter. [...] Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.

Is part of it about wanting a big SEP project in a post-ARM world?  Back-solving from the tech they want to fund?

Orion does not have enough propulsive capability to enter and return from LLO.

Offline theinternetftw

  • Full Member
  • *
  • Posts: 164
    • www.theinternetftw.com
  • Liked: 406
  • Likes Given: 220
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #79 on: 01/20/2018 07:42 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.

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

  • Member
  • Senior Member
  • *****
  • Posts: 16377
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 5257
  • Likes Given: 657
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

  • Member
  • Senior Member
  • *****
  • Posts: 16377
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 5257
  • Likes Given: 657
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

  • Senior Member
  • *****
  • Posts: 5478
  • Liked: 992
  • Likes Given: 653
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

  • Full Member
  • ****
  • Posts: 1350
  • Liked: 61
  • Likes Given: 3
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

  • Member
  • Posts: 59
  • Liked: 47
  • Likes Given: 10
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

  • Senior Member
  • *****
  • Posts: 5478
  • Liked: 992
  • Likes Given: 653
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

  • Full Member
  • ****
  • Posts: 465
  • USA
  • Liked: 174
  • Likes Given: 13
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

  • Senior Member
  • *****
  • Posts: 5478
  • Liked: 992
  • Likes Given: 653
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.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 2633
  • Fife
  • Liked: 1315
  • Likes Given: 1430
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #89 on: 02/24/2018 01:09 AM »
DSG - if you squint a little, looks moderately like a modern high power GEO comsat with a little more fuel and engines.
« Last Edit: 02/24/2018 03:51 AM by speedevil »

Offline Toast

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #90 on: 02/26/2018 11:27 PM »
Looks like in the budget proposal from a couple weeks back the Deep Space Gateway has been renamed the "Lunar Orbital Platform", the propulsion module now has funding attached to it ($504 million next year, $2.7 billion over five years), and the targeted launch date is actually being moved up to 2022. It is also now is planned for launch on a commercial vehicle instead of on the EM-2 SLS flight.

Offline mike robel

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2172
  • Merritt Island, FL
  • Liked: 229
  • Likes Given: 42
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #91 on: 02/27/2018 12:33 AM »
I see no benefit to sending what seems to be a sporadically inhabited outpost to the moon to do something that less expensive unmanned satellites could accomplish with less cost and greater coverage.

In my limited view, a more valid course of action would be to craft a spacecraft designed to last say 24 months in orbit to simulate a 6 month trip  to mars, 12 month  surface mission, and 6 month return, by a crew of 6 to 8 without resupply from Earth.  If things go wrong, they are minutes/hours from home and we could easily have a launch on need Falcon 9/Dragon or Atlas 5/CST booster on short notice for launch as well as an escape craft with the spacecraft.

Offline Space Ghost 1962

  • Senior Member
  • *****
  • Posts: 2783
  • Whatcha gonna do when the Ghost zaps you?
  • Liked: 2903
  • Likes Given: 2249
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #92 on: 02/27/2018 03:05 AM »
Suggest that the rationale for DSG/LOS is more about the missions/vehicles that would be passing through said way station than the way station itself. (The fact that it's being called a Lunar Orbital Station dooms it - doesn't need a DST, and there's no lander, so its just a "dead end" for NASA contractors to build, play with, and abandon, like ISS. Stillborn again.)

Otherwise why have a way station at all.

Like the original EM 1/2 missions for SLS, it is an unworthy gesture of the grand gesture of a national/international space program.

But then it says more about who and what we are, as a species, that we dither in such a silly way.

Plan your DST or lander or base (or all) as a complete vision. If it needs a way station, that follows out of the mission requirements and architecture. And only as much as is needed, so it doesn't become a "dead end".

There is no real commitment, just a show?

Offline AncientU

  • Senior Member
  • *****
  • Posts: 6217
  • Liked: 4011
  • Likes Given: 5547
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #93 on: 02/27/2018 10:55 AM »
Looks like in the budget proposal from a couple weeks back the Deep Space Gateway has been renamed the "Lunar Orbital Platform", the propulsion module now has funding attached to it ($504 million next year, $2.7 billion over five years), and the targeted launch date is actually being moved up to 2022. It is also now is planned for launch on a commercial vehicle instead of on the EM-2 SLS flight.

That's a steep 'initial' price tag for an SEP tug.
What part of the technology is so expensive?
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline woods170

  • IRAS fan
  • Senior Member
  • *****
  • Posts: 8400
  • IRAS fan
  • The Netherlands
  • Liked: 4801
  • Likes Given: 1520
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #94 on: 02/27/2018 11:06 AM »
Looks like in the budget proposal from a couple weeks back the Deep Space Gateway has been renamed the "Lunar Orbital Platform", the propulsion module now has funding attached to it ($504 million next year, $2.7 billion over five years), and the targeted launch date is actually being moved up to 2022. It is also now is planned for launch on a commercial vehicle instead of on the EM-2 SLS flight.

That's a steep 'initial' price tag for an SEP tug.
What part of the technology is so expensive?

No part. It's just that it will be done "NASA-style", much like SLS and Orion.
Remember: gravy train...
« Last Edit: 02/27/2018 11:07 AM by woods170 »

Offline AncientU

  • Senior Member
  • *****
  • Posts: 6217
  • Liked: 4011
  • Likes Given: 5547
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #95 on: 02/27/2018 11:31 AM »
Looks like in the budget proposal from a couple weeks back the Deep Space Gateway has been renamed the "Lunar Orbital Platform", the propulsion module now has funding attached to it ($504 million next year, $2.7 billion over five years), and the targeted launch date is actually being moved up to 2022. It is also now is planned for launch on a commercial vehicle instead of on the EM-2 SLS flight.

That's a steep 'initial' price tag for an SEP tug.
What part of the technology is so expensive?

No part. It's just that it will be done "NASA-style", much like SLS and Orion.
Remember: gravy train...

That kind of a price tag sure negates all the arguments about using SEP tugs to move bulk stuff around the Solar System.  Cannot imagine what 'bulk' commodities could afford a $2.7B* push.  Going so slow also implies each tug gets one (or maybe two) Mars payloads in its lifetime...

* Plus 'inflation'
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline brickmack

  • Full Member
  • ****
  • Posts: 465
  • USA
  • Liked: 174
  • Likes Given: 13
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #96 on: 02/27/2018 06:07 PM »
Being that most of the PPE options being bid are heavily derived from existing commercial comsats, with a lot of publicly available information on their pricing, it'll be interesting to see how they spin this as a sane expenditure

Offline Toast

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #97 on: 02/27/2018 06:30 PM »
Looks like in the budget proposal from a couple weeks back the Deep Space Gateway has been renamed the "Lunar Orbital Platform", the propulsion module now has funding attached to it ($504 million next year, $2.7 billion over five years), and the targeted launch date is actually being moved up to 2022. It is also now is planned for launch on a commercial vehicle instead of on the EM-2 SLS flight.

That's a steep 'initial' price tag for an SEP tug.
What part of the technology is so expensive?

Good question. NASA wants a really big system (50 kW), but that's still a pretty insane price tag. We should find out more soon, since NASA requested studies from five companies back in November that should be due to wrap up by March.

Offline DreamyPickle

  • Full Member
  • *
  • Posts: 188
  • Home
  • Liked: 80
  • Likes Given: 18
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #98 on: 02/27/2018 07:25 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

The SLS upper stage is hydrolox, isn't it impossible for it to last 3 days and relight for lunar orbit insertion? I know ULA's ACES claims to be able to do it but that's only after they develop IVF.

I also remember reading that NRHO was picked partly because of limited Orion delta-v, is that true?

On a related note, isn't it also very difficult to bring a SEP craft to lunar orbit Moon using only its own power? Switching the PPE to a commercial launch brings many new issues.
« Last Edit: 02/27/2018 11:35 PM by DreamyPickle »

Offline brickmack

  • Full Member
  • ****
  • Posts: 465
  • USA
  • Liked: 174
  • Likes Given: 13
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #99 on: 02/27/2018 08:25 PM »
The SLS upper stage is hydrolox, isn't it impossible for it to last 3 days and relight for orbit insertion? I know ULA's ACES claims to be able to do it but that's only after they develop IVF.

I also remember reading that NRHO was picked partly because of limited Orion delta-v, is that true?

On a related note, isn't it also very difficult to bring a SEP craft to lunar orbit Moon using only its own power? Switching the PPE to a commercial launch brings many new issues.

It wouldn't have to, TLI would be just a couple hours after LEO insertion. Orion does all later propulsion. There was a proposal for a Cryogenic Propulsion Stage (hence the name of Block 1's upper stage as the interim CPS) which would operate for weeks and could directly insert Orion and payload into LLO, but it fizzled. But even without ACES, ULA claims DCSS and Centaur could survive more than a week with only minor changes (namely a deployable solar shield). Its just that nobody has bought one, but it is advertised as a growth option in the payload planners guides (like Atlas V Heavy)

Difficult, but not impossible. SNC's PPE bid would include a close derivative used as a LEO-cislunar-LEO cargo vehicle, apparently using SEP for everything

Offline envy887

  • Senior Member
  • *****
  • Posts: 4502
  • Liked: 2439
  • Likes Given: 1367
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #100 on: 02/28/2018 05:09 PM »
On a related note, isn't it also very difficult to bring a SEP craft to lunar orbit Moon using only its own power? Switching the PPE to a commercial launch brings many new issues.

Either Falcon Heavy or Delta IV Heavy can put a 10 tonne PPE through TLI. It would only need to do LOI with SEP, which is quite feasible.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 5478
  • Liked: 992
  • Likes Given: 653
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #101 on: 02/28/2018 06:16 PM »
On a related note, isn't it also very difficult to bring a SEP craft to lunar orbit Moon using only its own power? Switching the PPE to a commercial launch brings many new issues.

It's certainly slower than using chemical propulsion as far as lunar-orbit insertion, but there's no rush.  SMART-1 went as far as GTO on chemical propulsion and from there went electric.
« Last Edit: 03/01/2018 02:39 PM by Proponent »

Offline speedevil

  • Senior Member
  • *****
  • Posts: 2633
  • Fife
  • Liked: 1315
  • Likes Given: 1430
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #102 on: 03/02/2018 11:51 AM »
On a related note, isn't it also very difficult to bring a SEP craft to lunar orbit Moon using only its own power? Switching the PPE to a commercial launch brings many new issues.

It's certainly slower than using chemical propulsion as far as lunar-orbit insertion, but there's no rush.  SMART-1 went as far as GTO on chemical propulsion and from there went electric.
Quote
Forty-two minutes after launch SMART-1 was placed into a geostationary transfer orbit, 742 x 36 016 km, inclined at 7° to the Equator.

Quote
The last firing of the EP before lunar capture was a thrust arc around the third lunar resonance, and ended on 14 October 2004. Apart from a 4 hour correction burn on 25 October, the EP remained inactive until lunar capture.
Up to 26 October, and the 289th engine pulse, the SMART-1 EP system had cumulated a total on time of nearly 3650 hours, consumed about 59 kg of xenon and imparted to the spacecraft a velocity increment of approximately 2735 ms-1 (9850 kmh-1).


Offline blasphemer

  • Full Member
  • *
  • Posts: 123
  • Slovakia
  • Liked: 56
  • Likes Given: 323
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #103 on: 03/03/2018 01:11 PM »
Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Why are "Lagrange Gateways" a terrible idea?

Offline UltraViolet9

  • Full Member
  • *
  • Posts: 109
  • Undisclosed
  • Liked: 143
  • Likes Given: 17
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #104 on: 03/03/2018 07:46 PM »
Why are "Lagrange Gateways" a terrible idea?

In the abstract, they are not.

If you want to park a large, expensive telescope a good distance from Earth and repair or upgrade it, a crew-tended habitat at a Lagrange Point is not a bad idea.

If you want to very efficiently (and very slowly) move lots of stuff long distances across the solar system, moving that stuff through Lagrange Points is about as efficient as you can get.  (Wiki "Interplanetary Transport Network".)

But for the foreseeable future, a Lagrange Gateway is a hammer in search of a nail. 

We don't have large, expensive, serviceable/upgradeable telescopes at Lagrange Points yet.  (JWST will be an exception in a couple or few years, hopefully, but it's not designed to be serviceable/upgradeable.)

And we're not trying to move lots of stuff very slowly but efficiently to Mars or anywhere else in the solar system yet.

All the other rationalizations for Lagrange Gateways or its cousin in DSG/LOP-G are specious.

Yes, you could get some deep space ops experience at such a gateway station before attempting a crewed Mars mission.  But such gateways are only crew tended for weeks to a few months.  You really need a year or so to properly simulate a Mars transit.

Yes, you could joystick some lunar rovers from such a gateway station.  But such gateways will only reduce the comm time delay from Earth by a few seconds.  Might as well keep your controllers in Pasadena or Houston.

Yes, you could stage some crewed lunar excursions from such a gateway station.  But you're going out of your way to do so.  If you want to go to the Moon, then go to the Moon.

Yes, you could stage crewed Mars missions from such a gateway station, especially if they rely on electric propulsion.  But there's no particular advantage versus staging from a high Earth orbit and then just passing through the same Lagrange point.  And there's no particular need for a "staging station" at either location.  If you want to go to Mars, then go to Mars.

DSG/LOP-G really grows out of the shortcomings of Orion/SLS. 

Orion doesn't have the delta-V to return from lower lunar orbits, so crewed lunar missions must stage out of a higher orbit.

And SLS doesn't have anywhere near the launch rate to support a traditional crewed Mars mission architecture like DRM 5.0, so NASA will have to rely on an unproven, high-power electric transit stage (the Deep Space Transport) to get to Mars with fewer launches.  The PPE on DSG/LOP-G is a step towards the DST's power/propulsion element.

In a more muscular, better coordinated, and much more efficient civil space program, a Lagrange Gateway would make some sense.

But we're using it's kissing cousin in DSG/LOP-G as a point solution band-aid to keep a deficient exploration architecture from falling apart.

We'd be much better off starting off with more and efficient capable launchers and transit vehicles and only inserting Lagrange stations or other waypoints when there's a unique need or clear advantage to doing so.

EDIT:  One more thought... opportunity cost is important to these considerations.  If a gateway costs, say, a billion dollars to put in place, it doesn't have to be perfectly justified.  You won't forgo much in the way of lunar or Mars missions to have that additional capability.

But with the first element (PPE) of DSG/LOP-G coming in at over $2.5 billion, we're looking at a gateway that will cost low tens of billions of dollars to field.  That money could buy a lot of lunar missions much sooner.  It's a very expensive and lengthy detour without a clear rationale (other than to help keep an Orion/SLS architecture from falling apart).  We can and should do better.
« Last Edit: 03/03/2018 08:24 PM by UltraViolet9 »

Offline ncb1397

  • Full Member
  • ****
  • Posts: 1002
  • Liked: 402
  • Likes Given: 3
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #105 on: 03/03/2018 08:21 PM »
Looks like in the budget proposal from a couple weeks back the Deep Space Gateway has been renamed the "Lunar Orbital Platform", the propulsion module now has funding attached to it ($504 million next year, $2.7 billion over five years), and the targeted launch date is actually being moved up to 2022. It is also now is planned for launch on a commercial vehicle instead of on the EM-2 SLS flight.

The funding line is for the whole station, not just the propulsion module. It looks to be about half the mass of skylab with them planning to spend under a third as much(<$5 billion).
« Last Edit: 03/03/2018 08:58 PM by ncb1397 »

Offline bodhiandphysics

  • Member
  • Posts: 5
  • Canada
  • Liked: 17
  • Likes Given: 3
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #106 on: 03/03/2018 10:28 PM »
Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Why are "Lagrange Gateways" a terrible idea?

To understand why they might be a terrible idea you have to understand why they may be a good idea.  If you're interested in going to Mars, it's probably a good idea to reuse some of that expensive hardware for multiple missions.  One obvious component to reuse is the transfer vehicle that gets you from earth orbit to Mars orbit.  This creates a problem, though in that this vehicle will need a lot of delta-v.  From a Mars Transfer Orbit (MTO) to low mars orbit (LMO) takes 2.5 km/s of delta-v so 5 both ways.  Early Mars ideas staged in LEO, but to get to a MTO from LEO requires 4 km/s of delta-v, so the whole mission would require an absolutely absurd 13 km/s of delta-v.  By contrast staging in a high earth orbit (and Lagrange Point is just a certain high earth orbit with an orbital period of 28 days) could lower this down to about 7 km/s of delta-v, which is manageable, particularly with a combination of chemical and electric propulsion, like the DSG would use.  Staging in a high orbit, however requires a large rocket to bring the various components, which happens to create a perfect role for the SLS (though presumably multiple Vulcan or Falcon Heavies could also be used).

There are other ways however of skinning this cat.  You can use aerobraking in mars and earth orbit to lower the delta v, but this makes it harder to build the vehicle and to reuse the vehicle (and also makes the mission much more dangerous). You can use ISRU on mars surface If you just want to go to Mars, the above architecture might be too complicated. Mars Direct doesn't stage at all!  It just lofts stuff to Mars and uses sacrificial aerobraking and Mars ISRU to make the numbers work. 

The advantage of staging in LOE, however, is that its easier to use reusable rockets to lift payload, and so the cost of payload in LOE might be orders of magnitude cheaper than in a higher orbit.  This is the basis of Spacex's mars plan which is based on aerobraking both in mars and earth orbit, as well as using ISRU extremely aggressively.  It's incredibly ambitious, but does give the advantage of amazing capability if it works. 

So staging at Lagrange point is fine and dandy!  A Langrange station might still be a dumb idea.  Why not just build the whole thing directly? Why use the intermediate step of the DSG?  The answer is that you need to test... to which the reply is  test in LOE which is going to be much cheaper than testing in a high orbit.  Here lies the second advantage of the Lagrange Gateway.  It's quite possible that during all the testing for the Mars mission, the political winds will change and the mission will be cancelled. If we're building the DSG, at least we get a moon mission out of all the mess.  Moon missions aren't bad? 

Of course, the DSG makes it much more likely that all we'll get is a moon mission.  And a) its a dumb moon mission, and b) we've already been to the moon!
 

Offline jongoff

  • Recovering Rocket Plumber/Space Entrepreneur
  • Senior Member
  • *****
  • Posts: 6184
  • Lafayette/Broomfield, CO
  • Liked: 2278
  • Likes Given: 772
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #107 on: 03/04/2018 02:56 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).

Yeah, but that would make too much sense.

~Jon

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 28384
  • Minnesota
  • Liked: 8253
  • Likes Given: 5447
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #108 on: 03/04/2018 03:01 AM »
It’s a shame the PPE won’t have enough power to send it somewhere interesting, like Mars or an asteroid. 250kW should do it.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 16377
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 5257
  • Likes Given: 657
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #109 on: 03/04/2018 04:59 AM »
Orion doesn't have the delta-V to return from lower lunar orbits, ...

Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.

Quote
And SLS doesn't have anywhere near the launch rate to support a traditional crewed Mars mission architecture like DRM 5.0, so NASA will have to rely on an unproven, high-power electric transit stage (the Deep Space Transport) to get to Mars with fewer launches.

Have you actually compared the number of SLS launches for both architectures? You can do a Mars mission from LEO using only three SLS Block II launches (first launch carries Orion, Hab and Lander/MAV in re-entry fairing, second and third launches refuel SLS upper stage for TMI). NASA's gateway plan requires a lot more launches than that.

Quote
b) we've already been to the moon!

We've also been to LEO, but we still keep going there. That's because its worthwhile to do so. Same with the Moon.
« Last Edit: 03/04/2018 04:59 AM by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline UltraViolet9

  • Full Member
  • *
  • Posts: 109
  • Undisclosed
  • Liked: 143
  • Likes Given: 17
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #110 on: 03/04/2018 06:58 AM »
Of course, another rocket would need to place Orion in LLO for this to work.

Of course.  Enter and return.

Quote
You can do a Mars mission from LEO using only three SLS Block II launches (first launch carries Orion, Hab and Lander/MAV in re-entry fairing, second and third launches refuel SLS upper stage for TMI).

DRM 5.0 assumes three Mars surface missions over a decade.  On that timeframe, the program could stockpile for one, but not several.

And even with stockpiling, the launch cadence for refueling could not be pulled off with the planned workforce and ground infrastructure.

Quote
NASA's gateway plan requires a lot more launches than that.

But it spaces out the launches, which is what SLS's extremely low launch cadence requires.

It's arse-backwards.  The launcher is driving the architecture instead of the other way around.

(And putting electric propulsion at an unproven order of magnitude on the critical path, to boot.)

Offline MATTBLAK

  • Elite Veteran & 'J.A.F.A'
  • Senior Member
  • *****
  • Posts: 4351
  • 'Space Cadets' Let us; UNITE!! (crickets chirping)
  • New Zealand
  • Liked: 1139
  • Likes Given: 2168
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #111 on: 03/04/2018 07:14 AM »
Orion doesn't have the delta-V to return from lower lunar orbits, ...

Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.

Quote
And SLS doesn't have anywhere near the launch rate to support a traditional crewed Mars mission architecture like DRM 5.0, so NASA will have to rely on an unproven, high-power electric transit stage (the Deep Space Transport) to get to Mars with fewer launches.

Have you actually compared the number of SLS launches for both architectures? You can do a Mars mission from LEO using only three SLS Block II launches (first launch carries Orion, Hab and Lander/MAV in re-entry fairing, second and third launches refuel SLS upper stage for TMI). NASA's gateway plan requires a lot more launches than that.

Quote
b) we've already been to the moon!

We've also been to LEO, but we still keep going there. That's because its worthwhile to do so. Same with the Moon.
Would that EDS also brake the group of spacecraft into Martian orbit, and return them later to Earth? Or would there have to be a Earth Return Stage(s), waiting there for them to send the Orion and Habitat back?
« Last Edit: 03/04/2018 07:14 AM by MATTBLAK »
"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

Offline Proponent

  • Senior Member
  • *****
  • Posts: 5478
  • Liked: 992
  • Likes Given: 653
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #112 on: 03/04/2018 03:08 PM »
But we're using it's kissing cousin in DSG/LOP-G as a point solution band-aid to keep a deficient exploration architecture from falling apart.

I like your entire post.  If I may generalize, what NASA and other space agencies like about LOP-G is that it's something they may actually be able to do within the political and financial constraints imposed upon them.  It suits the needs of space agencies, but it has little to do with exploring space.

If LOP-G really is the key to going to the moon or Mars, why does it not appear in the multitude of studies of lunar and martian architectures by NASA and others (e.g., ESAS in 2005 or the relatively recent Evolvable Mars Campaign)?

EDIT:  Deleted extraneous "of lunar architectures" after the closing parenthesis.  Added bolding and missing "of" in final sentence.
« Last Edit: 04/18/2018 12:50 PM by Proponent »

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8461
  • South coast of England
  • Liked: 339
  • Likes Given: 146
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #113 on: 03/04/2018 04:21 PM »
Orion doesn't have the delta-V to return from lower lunar orbits, ...

Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.
{snip}

A depot in LLO could refuel the Orion's service module.

Offline TrevorMonty

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #114 on: 03/04/2018 05:43 PM »
Orion doesn't have the delta-V to return from lower lunar orbits, ...

Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.
{snip}

A depot in LLO could refuel the Orion's service module.
In theory yes, but adds another potential point of failure. Having crew stuck in LLO because of  refuelling failure is not good outcome.

Offline ncb1397

  • Full Member
  • ****
  • Posts: 1002
  • Liked: 402
  • Likes Given: 3
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #115 on: 03/08/2018 01:45 AM »
Orion doesn't have the delta-V to return from lower lunar orbits, ...

Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.
{snip}

A depot in LLO could refuel the Orion's service module.
In theory yes, but adds another potential point of failure. Having crew stuck in LLO because of  refuelling failure is not good outcome.

You could always refuel in NRHO. Orion would use about 3300 kg of propellant to get into NRHO, be topped off to go to LLO and back (~1400-1500 m/s). It might be at a slight ~100 m/s deficit compared to a benchmark 100 km altitude circular orbit. Then it would just have to be fueled with about 2500 kg of propellant for the trip back to earth. Alternatively, it could be directed back to earth(TEI from LLO is about the same as LLO to NRHO(~750-800 m/s).

Or you could launch something else in the USA with a docking port to attach to the Orion. A lot of things would work to make up the modest 500 m/s deficit that Orion has to enter LLO and return to earth. A second SM with a docking port kit, a lunar descent stage equivalent in performence to th LEM descent module or even a ~8 mT chemical propulsion comsat with about 4200 kg of propellant(that it would need for GEO circularization - ~1.6 km/s, stationkeeping at 50 m/s per year anyway). The Block 1B is so overpowered for putting Orion alone into LLO that all kinds of not necessarily efficient schemes could work.

But what is the point with LLO really? It adds 1000 m/s of requirements on the Orion(vs NRHO), but subtracts 1000 m/s of requirements from the lander (vs staging at NRHO). The lander can be smaller and lighter compared to Orion that has to re-enter and support crew for longer durations and thus it could very well take less fuel to move the lander an extra 1 km/s vs move Orion an extra 1 km/s
« Last Edit: 03/08/2018 01:55 AM by ncb1397 »

Offline TrevorMonty

Re: Deep Space Gateway Power/Propulsion RFI
« Reply #116 on: 03/08/2018 02:13 AM »
Round trip for lander is 5.5km/s for NRO compared to 3.7km/s for LLO so extra 1.8km/s.  If DSG is already in place better to design lander to stage from.

Best to wait a few years and see what comes out of robotic exploration. With ISRU lunar refuelling lander only needs to be capable of 2.7km/s. Can be LH LOX as boil off is not an issue over a day.

The extra development costs of 5.5km/s lander compared to 2.7km/s would go long way to help pay for small ISRU plant.

Offline ncb1397

  • Full Member
  • ****
  • Posts: 1002
  • Liked: 402
  • Likes Given: 3
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #117 on: 03/08/2018 02:51 AM »
Round trip for lander is 5.5km/s for NRO compared to 3.7km/s for LLO so extra 1.8km/s.  If DSG is already in place better to design lander to stage from.

Best to wait a few years and see what comes out of robotic exploration. With ISRU lunar refuelling lander only needs to be capable of 2.7km/s. Can be LH LOX as boil off is not an issue over a day.

The extra development costs of 5.5km/s lander compared to 2.7km/s would go long way to help pay for small ISRU plant.

Post TLI, the manuevers are the following:

Apollo route:
LOI: ~1000 m/s
Descent: ~1800 m/s
Ascent: ~1800 m/s
Total: ~4600 m/s

DSG/LOP route:
lunar powered flyby: ~180 m/s
NRHO insertion: ~250 m/s
NRHO -> polar LLO: ~750 m/s
Descent: ~1800 m/s
Ascent: ~1800 m/s
LLO -> NRHO: ~750 m/s
Total: ~5530 m/s

differential: ~930 m/s

most numbers from:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019648.pdf

Your numbers assume the lander just appears in LLO with the LLO staging orbit. It doesn't count that the vehicle has to be transported from Earth(for the foreseeable future).
« Last Edit: 03/08/2018 02:54 AM by ncb1397 »

Offline Steven Pietrobon

  • Member
  • Senior Member
  • *****
  • Posts: 16377
  • Adelaide, Australia
    • Steven Pietrobon's Space Archive
  • Liked: 5257
  • Likes Given: 657
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #118 on: 03/08/2018 05:02 AM »
Would that EDS also brake the group of spacecraft into Martian orbit, and return them later to Earth? Or would there have to be a Earth Return Stage(s), waiting there for them to send the Orion and Habitat back?

The EDS only does TMI. Aerobraking is used to go into Mars orbit. The Hab has a rocket stage for TEI.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Joseph Peterson

  • Member
  • Posts: 94
  • Pittsburgh, PA
  • Liked: 38
  • Likes Given: 896
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #119 on: 03/08/2018 05:15 AM »
Orion doesn't have the delta-V to return from lower lunar orbits, ...

Yes it does. Orion has a delta-V of 1.2 km/s. That's sufficient for TEI from LLO. Of course, another rocket would need to place Orion in LLO for this to work.
{snip}

A depot in LLO could refuel the Orion's service module.
In theory yes, but adds another potential point of failure. Having crew stuck in LLO because of  refuelling failure is not good outcome.

You could always refuel in NRHO. Orion would use about 3300 kg of propellant to get into NRHO, be topped off to go to LLO and back (~1400-1500 m/s). It might be at a slight ~100 m/s deficit compared to a benchmark 100 km altitude circular orbit. Then it would just have to be fueled with about 2500 kg of propellant for the trip back to earth. Alternatively, it could be directed back to earth(TEI from LLO is about the same as LLO to NRHO(~750-800 m/s).

Or you could launch something else in the USA with a docking port to attach to the Orion. A lot of things would work to make up the modest 500 m/s deficit that Orion has to enter LLO and return to earth. A second SM with a docking port kit, a lunar descent stage equivalent in performence to th LEM descent module or even a ~8 mT chemical propulsion comsat with about 4200 kg of propellant(that it would need for GEO circularization - ~1.6 km/s, stationkeeping at 50 m/s per year anyway). The Block 1B is so overpowered for putting Orion alone into LLO that all kinds of not necessarily efficient schemes could work.

But what is the point with LLO really? It adds 1000 m/s of requirements on the Orion(vs NRHO), but subtracts 1000 m/s of requirements from the lander (vs staging at NRHO). The lander can be smaller and lighter compared to Orion that has to re-enter and support crew for longer durations and thus it could very well take less fuel to move the lander an extra 1 km/s vs move Orion an extra 1 km/s

I fully agree that the Lunar lander can be smaller and lighter compared to Orion.  What I don't understand is why the capacities of Orion are anything other than the limitation of one specific component of the larger transportation network.  Most of the mass that we'll need to send can take the slow road to LLO on SEP for a ~ 90% reduction in propellant mass.  It currently appears to me that increasing the lander Dv requirement by ~33% is going to dramatically increase total propellant requirements, or require development and operation of two separate lander classes, and an LLO depot for cargo landers.

Tangentially related:

I am looking for the thread on ideal Earth orbit transfer points for SEP tugs and search results have failed so far.  If no such thread exists, can someone help me identify the homework that needs to be done to justify thread creation?  I'm really curious just how much TLI(or any other destination) Dv can be transferred from Earth LVs.  100 km 86° LLO appears to be the best compromise to use for proper exploration of the Lunar poles while allowing access to other points of interest.  Fixing the Earth orbit departure point(Please let it be my hypothesized EML1-synchronous elliptical parking orbit with a perigee between 6000-10,000 km.) is required so that I can move beyond speculation about overall architecture mass budgets.  While speculation is fun, I prefer to know what I'm talking about.
If ZBLAN can't pay for commercial stations, we'll just have to keep looking until we find other products that can combine to support humans earning a living in space.

Offline envy887

  • Senior Member
  • *****
  • Posts: 4502
  • Liked: 2439
  • Likes Given: 1367
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #120 on: 03/16/2018 04:22 PM »
So is an RFP expected for the PPE? Or does that exist somewhere and I missed it?

The latest front page article mentions that the budget proposal indicates that the RFP will ask for the company proposing the PPE design will also commercially source a launch for it.

https://www.nasaspaceflight.com/2018/03/cislunar-station-new-name-presidents-budget/

Offline speedevil

  • Senior Member
  • *****
  • Posts: 2633
  • Fife
  • Liked: 1315
  • Likes Given: 1430
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #121 on: 03/16/2018 04:35 PM »
So is an RFP expected for the PPE? Or does that exist somewhere and I missed it?

The latest front page article mentions that the budget proposal indicates that the RFP will ask for the company proposing the PPE design will also commercially source a launch for it.

https://www.nasaspaceflight.com/2018/03/cislunar-station-new-name-presidents-budget/

Quote
“The targeted release of the draft solicitation will be in the April 2018 timeframe with final proposals anticipated to be due in the late July 2018 timeframe"

Offline Proponent

  • Senior Member
  • *****
  • Posts: 5478
  • Liked: 992
  • Likes Given: 653
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #122 on: 03/18/2018 02:35 PM »
But what is the point with LLO really? It adds 1000 m/s of requirements on the Orion(vs NRHO), but subtracts 1000 m/s of requirements from the lander (vs staging at NRHO). The lander can be smaller and lighter compared to Orion that has to re-enter and support crew for longer durations and thus it could very well take less fuel to move the lander an extra 1 km/s vs move Orion an extra 1 km/s

I have not thought through all of the implications of the whole range of possible lunar parking orbits, but off hand it seems to me the LLO probably offers more frequent return-to-Earth opportunities.  Certainly for near-equatorial landing sites, LLO gives an abort option every 2 hours.  For near-polar sites, if you have the delta-V for big plane changes (as was to be the case in Constellation), then you also have frequent abort options.

You could say that a rendezvous point at L1 or L2 gives you anytime abort.  But the catch is the getting from the lunar surface to the L-point is going to take about 3 days all by itself.  At some point, humanity is going to have to cut the cord and not worry about being able to beat a speedy return to Earth, but in the near term, taking a week or so to get home might seem risky.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 5478
  • Liked: 992
  • Likes Given: 653
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #123 on: 03/18/2018 03:01 PM »
While speculation is fun, I prefer to know what I'm talking about.

Always a good idea!

Quote
I am looking for the thread on ideal Earth orbit transfer points for SEP tugs and search results have failed so far.  If no such thread exists, can someone help me identify the homework that needs to be done to justify thread creation?  I'm really curious just how much TLI(or any other destination) Dv can be transferred from Earth LVs.  100 km 86° LLO appears to be the best compromise to use for proper exploration of the Lunar poles while allowing access to other points of interest.  Fixing the Earth orbit departure point(Please let it be my hypothesized EML1-synchronous elliptical parking orbit with a perigee between 6000-10,000 km.) is required so that I can move beyond speculation about overall architecture mass budgets.

I don't understand what you mean by transferring TLI delta-V.  But if we're talking about using electric propulsion to get things to the moon, the most efficient thing to do (i.e., the thing that would make most use of electric propulsion and the least use of chemical) would be to shift from chemical to electric in LEO.  The delta-V needed for a constant-low-thrust transfer between two circular orbits is simply the difference in the circular velocities of the two orbits.  You can think of escape as being a circular orbit at infinity, i.e., one with a circular velocity of zero.  TLI is a little bit short of escape, but the difference is not large.

The inclination of the lunar orbit has little impact on the delta-V needed.  The moon's radius being about 1738 km, the difference between aiming for lunar equatorial orbit and lunar polar orbit at an altitude of 100 km is only about (1738 km + 100 km)/(384,400 km) = 0.00452 radians = 0.259 degrees.

Offline Joseph Peterson

  • Member
  • Posts: 94
  • Pittsburgh, PA
  • Liked: 38
  • Likes Given: 896
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #124 on: 03/21/2018 06:04 AM »
While speculation is fun, I prefer to know what I'm talking about.

Always a good idea!

Quote
I am looking for the thread on ideal Earth orbit transfer points for SEP tugs and search results have failed so far.  If no such thread exists, can someone help me identify the homework that needs to be done to justify thread creation?  I'm really curious just how much TLI(or any other destination) Dv can be transferred from Earth LVs.  100 km 86° LLO appears to be the best compromise to use for proper exploration of the Lunar poles while allowing access to other points of interest.  Fixing the Earth orbit departure point(Please let it be my hypothesized EML1-synchronous elliptical parking orbit with a perigee between 6000-10,000 km.) is required so that I can move beyond speculation about overall architecture mass budgets.

I don't understand what you mean by transferring TLI delta-V.  But if we're talking about using electric propulsion to get things to the moon, the most efficient thing to do (i.e., the thing that would make most use of electric propulsion and the least use of chemical) would be to shift from chemical to electric in LEO.  The delta-V needed for a constant-low-thrust transfer between two circular orbits is simply the difference in the circular velocities of the two orbits.  You can think of escape as being a circular orbit at infinity, i.e., one with a circular velocity of zero.  TLI is a little bit short of escape, but the difference is not large.

The inclination of the lunar orbit has little impact on the delta-V needed.  The moon's radius being about 1738 km, the difference between aiming for lunar equatorial orbit and lunar polar orbit at an altitude of 100 km is only about (1738 km + 100 km)/(384,400 km) = 0.00452 radians = 0.259 degrees.

Thanks for the reply.  Hopefully I can rephrase my question in a more intelligible manner.

SEP provides a ~90% reduction in required propellant mass.  I want to argue in favor of is a version of chemical limbo, or 'how low can you go.'  SEP's primary limitation in Earth orbit is the inner Van Allen belts, or a perigee of 6.000-10,000 km.  There should exist an elliptical parking orbit with a perigee of ~10,000 km that allows for 2nd stage disposal/recovery, and, maximizes total payload to Lunar orbit, while, allowing support of dozens of Lunar landings per Earth year.  What I want to know is if anyone has already done the math to find out where we can expect ideal cargo staging points are?

If not, I'll be asking for help checking my methodology.
If ZBLAN can't pay for commercial stations, we'll just have to keep looking until we find other products that can combine to support humans earning a living in space.

Offline Ronsmytheiii

  • Moderator
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 22469
  • Liked: 792
  • Likes Given: 294
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #125 on: 08/08/2018 06:38 PM »
Seems applicable:

Quote
Space Systems/Loral, L.L.C., (SSL) in Palo Alto, California, $2 million
  Proposal: In-Space Xenon Transfer for Satellite, Servicer and Exploration Vehicle Replenishment and Life Extension

https://www.nasa.gov/press-release/nasa-announces-new-partnerships-to-develop-space-exploration-technologies
And this is a good reminder that just because one of your fellow space enthusiasts occasionally voices doubts about the SpaceX schedule announcements or is cautious about believing SpaceX has licked a problem before actually seeing proof that's true, it doesn't mean they hate SpaceX.

Offline DreamyPickle

  • Full Member
  • *
  • Posts: 188
  • Home
  • Liked: 80
  • Likes Given: 18
Re: Deep Space Gateway Power/Propulsion RFI
« Reply #126 on: 08/14/2018 05:35 PM »
Shouldn't this thread be moved to the moon section with the rest of LOP-G? It's especially silly to have this in the SLS section when there's talk of moving it to a commercial launch.

Tags: