Author Topic: Deep Space Gateway Power/Propulsion RFI  (Read 16281 times)

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.

Offline A_M_Swallow

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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.

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