Author Topic: Deep Space Gateway Power/Propulsion RFI  (Read 12827 times)

Offline theinternetftw

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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 »


Offline brickmack

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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

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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.
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Offline theinternetftw

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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

Offline yg1968

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Offline Propylox

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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

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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

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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

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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

Online envy887

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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.

Offline oldAtlas_Eguy

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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.

Online 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

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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

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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

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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.

Offline jgoldader

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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

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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

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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

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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

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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 »

Offline oldAtlas_Eguy

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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

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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

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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

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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

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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

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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

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #28 on: 07/23/2017 08:04 AM »
Don't feed the troll...

Offline oldAtlas_Eguy

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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

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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.

Offline oldAtlas_Eguy

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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. 

Offline oldAtlas_Eguy

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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.

Offline oldAtlas_Eguy

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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

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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

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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

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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 »

Offline oldAtlas_Eguy

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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

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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

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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

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Re: Deep Space Gateway Power/Propulsion RFI
« Reply #51 on: 07/29/2017 03:17 PM »
How do you know it is not wanted?

Offline BrightLight

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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)

Offline BrightLight

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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

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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

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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

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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.

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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

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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

Offline Jim

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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

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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

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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

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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

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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

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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

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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 »

Online Ben the Space Brit

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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!)
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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

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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.

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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.

Offline oldAtlas_Eguy

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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.

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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

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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.

Offline oldAtlas_Eguy

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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

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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 »

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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.

Offline oldAtlas_Eguy

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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.

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