Author Topic: Mars Orbital mission with only DSH and Orion  (Read 6899 times)

Offline ncb1397

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Mars Orbital mission with only DSH and Orion
« on: 06/04/2016 05:18 PM »
Basic components:

Orion with upgraded SM
40 mT fuel
9 mT SM
10 mT CM
59 mT total
300 isp hypergolic engine

DSH
5 mT xenon
5 mT solar array
15 mT habitation, docking ports and water/fuel tanks
5 mT food and logitics
5 mT water for shielding and drinking
total: 35 mT
3000 isp electric engine

Interplanetary spacecraft is 3 orions as chemical tugs and 1 DSH. TMI, orbital insertion at mars and TEI is done chemically with Orion. Total mass is 212 mT.

The 3 orions provide the following delta V to yield the 3.1 km/s total mission propulsive delta v for ~GTO -> Mars high elliptical orbit -> Earth doing a direct entry at Earth.

1st orion(expended after fuel used up): 212 mT/ 172 mT mass ratio for delta V of 615 m/s
2nd orion(expended after fuel used up):153 mT/ 113 mT mass ratio for delta V of 891 m/s
3rd orion(kept in stack after burn to do earth re-entry): 94 mT / 54 mT mass ratio for delta V of 1630 m/s
total delta V: 3136 m/s

The mission would require 4 launches(1 DSH, 3 Orions) to sub-GTO on an SLS 1B. They will be auto-docked together with the last launch carrying crew. DSH would use SEP to raise orbit to an elliptical earth orbit higher energy than GTO before departure. The Orion tugs can do all the mission maneuvers chemically from GTO, but starting from a higher orbit adds margins. Additionally, the barely used SEP system adds margins and allows for some maneuvering in mars orbit.

Some upgrades possible are a methane/oxygen cryogenic service module for orion which will allow for higher isp and supplying oxygen, water, heat and power from the propellant tanks for contingencies or mission planning. The ideal would be a hydrogen/oxygen cryogenic SM with fuel cells but ZBO may not be technically feasible. Additionally, the DSH could be upgraded for nuclear power and NEP or upgraded with better isp electric engines or higher specific power solar panels.

A quick picture of the stack configuration once configured for interplanetary flight:
https://docs.google.com/drawings/d/1b_ahutB8E5n7fBE4IIswQE9UoqEu5nmBWCJy4HZjFlY/edit?usp=sharing
« Last Edit: 06/04/2016 05:20 PM by ncb1397 »

Offline redliox

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Re: Mars Orbital mission with only DSH and Orion
« Reply #1 on: 06/04/2016 08:02 PM »
Although improving Orion's SM is a good idea, 3 Orions plus a DSH isn't going to suffice. I've crunched a few numbers before with it; Orion is a leadweight beyond Earth orbit. Using electric propulsion to put the DSH in high orbit is good as would be using it en route to Mars, but SEP is also too sluggish to sufficiently help in larger maneuvers.  Using 3 Orions versus just 2 exclusively near Earth isn't efficent enough.
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Offline Chilly

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Re: Mars Orbital mission with only DSH and Orion
« Reply #2 on: 06/07/2016 03:29 PM »
I ranted about something along these lines at my own blog a couple of months ago (https://chilesfiles.wordpress.com/2016/04/22/halfway-to-nowhere/#more-2489). I'd dearly love to see NASA take advantage of the 2021 free-return window as outlined by the Inspiration Mars crowd. If we can't afford to launch SLS much more than once a year, then let's make it count for something before the whole thing is steamrolled into obsolescence by the private sector.
A manned flyby of Venus and Mars would be an audacious and extremely valuable proof-of-concept mission. There's a golden opportunity here for a one-off, Apollo 8-style home run if we only had the stones to pursue it. But that would require focused leadership and political will to see it through over a couple of election cycles.
Therefore, it won't happen. But damn if it wouldn't be glorious.
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Offline Khadgars

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Re: Mars Orbital mission with only DSH and Orion
« Reply #3 on: 07/11/2016 10:58 PM »
What about doing this for the EVME Free Return Trajectory in 2021? 

Offline Chilly

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Re: Mars Orbital mission with only DSH and Orion
« Reply #4 on: 07/11/2016 11:01 PM »
Pretty sure that's what I was advocating...
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Offline guckyfan

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Re: Mars Orbital mission with only DSH and Orion
« Reply #5 on: 07/13/2016 01:25 PM »
The return speed for the free return trajectory is quite high. Higher than a normal Mars return. Pretty sure Orion cannot handle it for a direct EDL. Could Orion brake to capture and then reach L1 without service module?

Offline brickmack

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Re: Mars Orbital mission with only DSH and Orion
« Reply #6 on: 07/15/2016 11:15 PM »
Orion is only rated for 1 year in space anyway, even if it could survive reentry from a Mars return trajectory its not certified to carry people on such a long duration mission. This is why most of the notional Mars proposals so far using SLS leave Orion behind in cislunar orbit

Offline KelvinZero

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Re: Mars Orbital mission with only DSH and Orion
« Reply #7 on: 07/16/2016 07:04 AM »
Instead of generic ion engines, how about multiple instances of the SEP tug? I have seen images implying it would stack nicely and even is designed to do so. I think this is more in line with the OP's goal of working with what we have (though I admit the term 'have' is a bit flexible here :) )

We could have the DSH being tested out for a few years in high lunar orbit. We could have several SEP tugs visiting asteroids or whatever, and perhaps time the mars orbit mission for the point at which we have most trust in the hardware: not too new, not to old.

My layman's feeling is that a single orion would be best, just for the initial push with whatever propellant it can reasonably have on arrival at the DSH, then keep the command module and perhaps immediately dump the service module. Use electric thrust for the rest and aim for Deimos due to it being easier in terms of delta-v.

Perhaps the DSH orbit could be nudged into a near earth approach before the mission begins to exploit Oberth effect for this one small burn.

About this Orion one year and speed of earth reentry issue, how big a job is that to fix? Seems to me that if we are going to build that Orion thing we should at least have an upgrade path planned. It doesn't need to be the first Orion that flies, but this would have to be a few years later (after the DSH and SEP tug shakedown mentioned)
« Last Edit: 07/16/2016 07:05 AM by KelvinZero »

Online A_M_Swallow

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Re: Mars Orbital mission with only DSH and Orion
« Reply #8 on: 07/16/2016 06:01 PM »
Instead of generic ion engines, how about multiple instances of the SEP tug? I have seen images implying it would stack nicely and even is designed to do so. I think this is more in line with the OP's goal of working with what we have (though I admit the term 'have' is a bit flexible here :) )

We could have the DSH being tested out for a few years in high lunar orbit. We could have several SEP tugs visiting asteroids or whatever, and perhaps time the mars orbit mission for the point at which we have most trust in the hardware: not too new, not to old.

My layman's feeling is that a single orion would be best, just for the initial push with whatever propellant it can reasonably have on arrival at the DSH, then keep the command module and perhaps immediately dump the service module. Use electric thrust for the rest and aim for Deimos due to it being easier in terms of delta-v.

Perhaps the DSH orbit could be nudged into a near earth approach before the mission begins to exploit Oberth effect for this one small burn.

About this Orion one year and speed of earth reentry issue, how big a job is that to fix? Seems to me that if we are going to build that Orion thing we should at least have an upgrade path planned. It doesn't need to be the first Orion that flies, but this would have to be a few years later (after the DSH and SEP tug shakedown mentioned)

The problem with that is the Orion Service Module supplies the crew with oxygen and water. The Command Module can only support life for a few hours.
https://en.wikipedia.org/wiki/Orion_Service_Module

Offline KelvinZero

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Re: Mars Orbital mission with only DSH and Orion
« Reply #9 on: 07/16/2016 11:16 PM »
The problem with that is the Orion Service Module supplies the crew with oxygen and water. The Command Module can only support life for a few hours.
https://en.wikipedia.org/wiki/Orion_Service_Module
That is enough, isn't it? I was imagining all/most of the lifesupport on the DSH, and direct return to earth.

I admit I really hadn't been keeping up with what this service module is. I also hadn't thought about whether whatever tiny thrusters the command module has are enough to arrange it to enter the earth's atmosphere while the DSH passes by.

What is it that limits the Orion to one year in space? I imagined that fundamental problems were more likely in the inaccessibility of the service module, and that command module issues could be solved without massive redesign?

Offline Bob Shaw

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Re: Mars Orbital mission with only DSH and Orion
« Reply #10 on: 07/16/2016 11:52 PM »
I ranted about something along these lines at my own blog a couple of months ago (https://chilesfiles.wordpress.com/2016/04/22/halfway-to-nowhere/#more-2489). I'd dearly love to see NASA take advantage of the 2021 free-return window as outlined by the Inspiration Mars crowd. If we can't afford to launch SLS much more than once a year, then let's make it count for something before the whole thing is steamrolled into obsolescence by the private sector.
A manned flyby of Venus and Mars would be an audacious and extremely valuable proof-of-concept mission. There's a golden opportunity here for a one-off, Apollo 8-style home run if we only had the stones to pursue it. But that would require focused leadership and political will to see it through over a couple of election cycles.
Therefore, it won't happen. But damn if it wouldn't be glorious.


I take your point, though the comparison to Apollo 8 is somewhat false; however, in view of the declared intent of SpaceX to not merely go to Mars, but to land a sort-of-human-rated spacecraft there within the next few years (SLS notwithstanding) it is probably too late to rescue SLS/Orion with a 'death or glory' shot. Wouldn't it be a nice demo, however, to have Red Dragon land on Mars and deploy a rover which was controlled in real-time by the crew of an Orion looping past Mars... ...but that won't happen.

Offline RonM

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Re: Mars Orbital mission with only DSH and Orion
« Reply #11 on: 07/17/2016 03:30 PM »
Interesting thing about all this Orion/SLS and MCT planning is the timeframe. SpaceX is planning BFS Mars missions in the 2020s, as early as 2024. NASA is planning Mars missions in the 2030s and 2040s. During the 2020s NASA will be conducting cislunar tests.

If SpaceX is successful, then NASA can join in on SpaceX missions to Mars and either cancel Orion/SLS or use it for lunar or asteroid missions.

If SpaceX fails to get BFS off the ground, then NASA can continue on with its Orion/SLS program.

If both organizations fail, we're just back to the status quo.

Both organizations should keep working on their projects and see what happens. We're in a better situation of someone getting to Mars than ever before.

Getting back to the OP, three Orion spacecraft on a single mission isn't practical. One SLS launch for the crew in an Orion and the other two launches can be propulsion modules.

Offline Arb

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Re: Mars Orbital mission with only DSH and Orion
« Reply #12 on: 07/17/2016 10:46 PM »
If SpaceX is successful, then NASA can ... either cancel Orion/SLS or use it for lunar or asteroid missions.

A nit but an important one. NASA cannot cancel SLS; only Congress can do that.


Offline tea monster

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Re: Mars Orbital mission with only DSH and Orion
« Reply #13 on: 07/17/2016 10:51 PM »
Instead of 3 Orions, why not have another ICPS for boost operations?

Offline RonM

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Re: Mars Orbital mission with only DSH and Orion
« Reply #14 on: 07/18/2016 02:21 AM »
If SpaceX is successful, then NASA can ... either cancel Orion/SLS or use it for lunar or asteroid missions.

A nit but an important one. NASA cannot cancel SLS; only Congress can do that.

Yes, thanks for pointing that out.

Offline Zed_Noir

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Re: Mars Orbital mission with only DSH and Orion
« Reply #15 on: 07/18/2016 03:52 AM »
If SpaceX is successful, then NASA can ... either cancel Orion/SLS or use it for lunar or asteroid missions.

A nit but an important one. NASA cannot cancel SLS; only Congress can do that.

Yes, thanks for pointing that out.

Slightly OT query. If the SpaceX architecture works than who get the final say in who gets to ride along, since it will not be a NASA mission?



Online AncientU

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Re: Mars Orbital mission with only DSH and Orion
« Reply #16 on: 07/18/2016 03:53 PM »
How are we going to have even one human qualified Orion, a few SLS launches, or an SEP tug by 2021?
« Last Edit: 07/18/2016 03:55 PM by AncientU »
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Re: Mars Orbital mission with only DSH and Orion
« Reply #17 on: 07/18/2016 05:11 PM »
How are we going to have even one human qualified Orion, a few SLS launches, or an SEP tug by 2021?

The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.

The tug design may need upgrading to reach human rating standards.

Offline Jim

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Re: Mars Orbital mission with only DSH and Orion
« Reply #18 on: 07/18/2016 05:26 PM »

The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.

The tug design may need upgrading to reach human rating standards.

NASA can buy SEP tugs now if it wants to.  See Dawn.


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Re: Mars Orbital mission with only DSH and Orion
« Reply #19 on: 07/18/2016 06:39 PM »

The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.

The tug design may need upgrading to reach human rating standards.

NASA can buy SEP tugs now if it wants to.  See Dawn.



Good machine Dawn. However its SEP is not a heavy.

Online notsorandom

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Re: Mars Orbital mission with only DSH and Orion
« Reply #20 on: 07/19/2016 07:41 PM »
There is no need to bring any Orions along for the ride. A simple mission like this could be staged out of L1, L2, or DRO. Have the crew launch on Orion out there to meet the Mars bound spacecraft. The return the crew to one of these places to meet up with a waiting return craft. The interplanetary craft would consist of the DSP, SEP tug, and possibly a hypergolic chemical propulsion system. The same SEP tug could raise the interplanetary craft out of LEO where it could be assembled using smaller launch vehicles.

Offline KelvinZero

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Re: Mars Orbital mission with only DSH and Orion
« Reply #21 on: 07/20/2016 06:30 AM »
There is no need to bring any Orions along for the ride. A simple mission like this could be staged out of L1, L2, or DRO. Have the crew launch on Orion out there to meet the Mars bound spacecraft. The return the crew to one of these places to meet up with a waiting return craft.
Doesn't that imply either that the Orion can survive in space for the duration of the mission anyway, or an additional launch of an Orion, probably on an SLS? Also an extra rendezvous in either case.

How much mass would the Orion add, proportionally? I had assumed the DSH was fairly big, so the Orion would only add a bit of inefficiency. You add 25% more volume say, and that 25% is 1/3 heavier than if it had been designed purely for in-space.. something like that. Those numbers are pulled out of a hat..anyone got better ones?

Offline MATTBLAK

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Re: Mars Orbital mission with only DSH and Orion
« Reply #22 on: 07/20/2016 08:23 AM »
Orion could only go along, all the way to Mars, if it had a heatshield and other, multiple systems upgrades. If there were a Gateway Station at L-2, then the Orion would only need to go that far - taking crews to and from the DSH and other Mars-bound components. The other, famous capsule craft we all know about (;)) is supposed to be able to withstand a good, long 2-year 'space soak' and is also supposed to have a heatshield good enough to withstand a direct Earth entry, coming back from deep space.

If the Orion was to act as a Mars Mission 'Command & Control Module' and Earth Return Vehicle, then it's likely it's Service Module would need upgrades and increased propellant loads and both the CM & SM would need redesign so their hypergolic propulsion systems wouldn't degrade from more than 12 months in deep space. Such upgrades to Orion wouldn't come cheap - and would that be a 'Block III' or IV version of the craft? And would it need to perform a fair sized 'slow down' burn to make it safely down to Earth?
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Offline RonM

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Re: Mars Orbital mission with only DSH and Orion
« Reply #23 on: 07/20/2016 02:12 PM »
Since NASA isn't planning on going to Mars until the 2030s, there is plenty of time for Orion upgrades if needed.

I prefer the idea of a gateway station, but it might not fit NASA's budget. Earlier Mars mission plans did have Orion as the "command and control module."

Satellites and probes use hypergolic systems for very long mission durations. They don't degrade in 12 months.

No need for a slow down burn with a proper heatshield.

If "the other famous capsule" can be built to solve these issues, then why can't Orion be upgraded?

Offline the_other_Doug

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Re: Mars Orbital mission with only DSH and Orion
« Reply #24 on: 07/20/2016 02:54 PM »
Guys?  A lot of us non-engineers are playing Kerbal with this -- we're taking one or two statements from various sources, out of context, and pretending that they are in the little postage-stamp listing of capabilities and limitations of the building blocks we're looking at with Orion and NASA's Mars architecture.

The discussion is also just playing with one or two elements -- a heat shield that has not been rated or tested at the high end of direct entry from a Mars transfer orbit, for example, and an Orion SM that can't support the spacecraft for more than a month or two, and as such, the remaining systems aren't tweaked to be able to shut down for long stretches and then brought back online.  And that's because these systems were never designed to operate for years at a time without being attached to a larger architecture.

The basic Orion design does not in any way preclude the relatively minor tweaks needed to support bringing an Orion along all the way to LMO and back.  This does not require a thorough redesign of the spacecraft systems.  If, indeed (for example), the current Orion heat shield material won't survive projected worst-case direct entry speeds, then we have, what, another 10 years to develop, test and implement a heat shield that can do so.  It won't be needed for at least a decade, per NASA's funding-starved schedules.  Even the proposed Orion+DSH mission being discussed here wouldn't launch for another eight years -- still plenty of time to develop the heat shield and other tweaks needed, if one chose to fly this mission.

So, it's just as disingenuous to state, as of 2016, that Orion is not capable of coming back from Mars (and making the logical error of extending that to say that, therefore, Orion will never be capable of it) as it is to say that Dragon is not currently capable of propulsive landings, and therefore will never be capable of them.  See my point?

And to counter the argument "Well, SpaceX is planning for propulsive entries, but NASA doesn't have any plans to beef up Orion's heat shield," I will just say that NASA currently plans to bring Orion to LMO and back, and the DRM currently includes a direct entry of the Orion from the trans-Earth trajectory.  Using just a little logic (a skill some of us could use to learn), we see that NASA cannot be planning what they are planning unless they are also planning on applying all mods to Orion (including to the heat shield) that are needful to accomplish the mission.

Also, NASA, at least, is always all about contingencies and abort modes, when it comes to placing humans in space.  I can think of a number of different trans-Earth coast abort modes that would make it nearly impossible to maneuver to a rendezvous with the only thing capable of surviving entry into Earth's atmosphere in cislunar space, but does leave you the ability to aim with some precision at a direct entry corridor.  (And no -- don't even start with "Then we just send a <insert non-Orion entry capsule name here> to rendezvous with the incoming spacecraft."  Just try modeling that kind of trajectory -- you'd either need to launch such a rescue vehicle years before you launch the Orion to Mars, just in case, or you'd need several BFSes all connected together to get something into the same inbound trajectory without starting out at Mars in the first place.)

I wouldn't want to be heading back to Earth from Mars, in a spacecraft that cannot enter an atmosphere, when my main propulsion goes out and I am reduced to the choices of shooting off into solar orbit, or at least having my constituents return to Earth in a blazing fireball.

For safety reasons and for contingency planning to reduce the likelihood of loss of crew, any spacecraft they bring back from Mars with people in it will have the ability to bring those people directly back through the atmosphere, to a safe landing on Earth.  If that's not the Orion, then they will feel forced to develop, at much greater expense, a lifeboat or escape pod configuration that gives the crew a way to come back without needing to rendezvous with a return vehicle.

Now, balance the expense and complication of developing such a lifeboat against simply upgrading Orion's heat shield (and tweaking the SM's systems to support quiescent hibernation for periods of up to three years) and taking it to Mars and back.

I'll bet you anything that applying the needed tweaks to Orion come out to be far more economical than any other approach.  And, bottom line, I just cannot see NASA bringing people back from Mars in a ship that cannot guarantee their safe return without any additional self-powered rendezvous maneuvers.  It would add a lot of potential single-point failures that could result in complete LOCV.  And that's the one thing I can't see NASA ever doing...
-Doug  (With my shield, not yet upon it)

Online Robotbeat

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Re: Mars Orbital mission with only DSH and Orion
« Reply #25 on: 07/20/2016 06:26 PM »
Hey, engineers of the past would've KILLED for a simulator like Kerbal. ;)
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Re: Mars Orbital mission with only DSH and Orion
« Reply #26 on: 07/20/2016 07:19 PM »
Hey, engineers of the past would've KILLED for a simulator like Kerbal. ;)

Kerbal may not be perfect but it allows engineers to experiment cheaply and gets rid of the the silly options. Its outfeeds allow more detailed simulators to start with a good second approximation.

Online AncientU

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Re: Mars Orbital mission with only DSH and Orion
« Reply #27 on: 07/20/2016 09:41 PM »

The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.

The tug design may need upgrading to reach human rating standards.

NASA can buy SEP tugs now if it wants to.  See Dawn.

Is a 0.09Newton (0.02lbf) 'SEP tug' for a 212 tonne (466,400lb) mission a bit undersized for a manned mission in deep space rad environment?
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Re: Mars Orbital mission with only DSH and Orion
« Reply #28 on: 07/21/2016 01:53 AM »

The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.

The tug design may need upgrading to reach human rating standards.

NASA can buy SEP tugs now if it wants to.  See Dawn.

Is a 0.09Newton (0.02lbf) 'SEP tug' for a 212 tonne (466,400lb) mission a bit undersized for a manned mission in deep space rad environment?
The NSTAR thruster is fairly low-power at 2.3kW. But commercial units are at least 4.5kW and can be ganged together. And the NEXT thruster is 7kW. Gang 15 together, and you have >100kW, which is good enough for a basic tug.
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Online Mark S

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Re: Mars Orbital mission with only DSH and Orion
« Reply #29 on: 07/21/2016 03:35 PM »

The back end of the Asteroid Redirect Robotic Mission (ARRM) spacecraft is a Solar Electric Propulsion (SEP) tug. This is due to be launched in December 2021. So by about 2021 NASA will be able to buy SEP tugs.

The tug design may need upgrading to reach human rating standards.

NASA can buy SEP tugs now if it wants to.  See Dawn.

Is a 0.09Newton (0.02lbf) 'SEP tug' for a 212 tonne (466,400lb) mission a bit undersized for a manned mission in deep space rad environment?
The NSTAR thruster is fairly low-power at 2.3kW. But commercial units are at least 4.5kW and can be ganged together. And the NEXT thruster is 7kW. Gang 15 together, and you have >100kW, which is good enough for a basic tug.

I'm not sure why you're quoting power consumption when AncientU's question was about thrust. I suppose a ~46x increase in power consumption would translate to a similar increase in thrust. Assuming an increase in efficiency (NEXT over NSTAR) between 0% and 100%,  that would still only come out to somewhere between 0.9 and 1.8 lbf of total thrust. Would that be suitable for a 212 tonne mission stack? What would the Mars transit time be, assuming constant thrust?

Thanks.

Online Robotbeat

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Re: Mars Orbital mission with only DSH and Orion
« Reply #30 on: 07/21/2016 05:30 PM »
Power and thrust are proportional to each other, and the proportionality constant is exhaust velocity. THAT'S why I said power.

Power = thrust*exhaustvelocity
« Last Edit: 07/21/2016 05:48 PM by Robotbeat »
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Online Mark S

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Re: Mars Orbital mission with only DSH and Orion
« Reply #31 on: 07/21/2016 07:46 PM »
Power and thrust are proportional to each other, and the proportionality constant is exhaust velocity. THAT'S why I said power.

Power = thrust*exhaustvelocity

Thanks, that (proportionality) is pretty much what I figured, as you can see from my post. However, now I'm curious as to the power ratings of the thrusters that you mentioned. Is that the power output of the thruster, using the equation you gave? Or is it the electrical power input required to operate the thruster at the given thrust level? When you stated the thrusters' power levels in watts, I thought it was the latter. Given the context of your reply, it would seem to be the former.

Anyway, the bottom line seems to be that you need ~1 MW of power for every 10 lbf of thrust. Please correct me if my math is wrong, or if I have a bad understanding of the underlying principles.

Thanks again.

Online A_M_Swallow

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Re: Mars Orbital mission with only DSH and Orion
« Reply #32 on: 07/21/2016 09:25 PM »
Ion Thruster Information

NSTAR

Propellant Xenon
Power 2.3 kW
Isp 3,300 to 1,700 s
Max Thrust 92 mN

NEXT

Propellant Xenon
Power 6.9 kW
Isp 4,190 s
Max Thrust 236 mN

Ref: https://en.wikipedia.org/wiki/Ion_thruster

On interplanetary trips solar power is not constant. This affects both the design of the spacecraft and route planning. Power from the solar panels drops to (nearly) zero when in the shadow of the Earth or Mars. The time in shadow per orbit varies with height. The power received from the sun falls off according to an inverse square law.

Solar power at Earth orbit 1,413 Wm-2
Solar power at Mars orbit 715 Wm-2

Ref: https://en.wikipedia.org/wiki/Sunlight

Online Robotbeat

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Re: Mars Orbital mission with only DSH and Orion
« Reply #33 on: 07/22/2016 07:30 PM »
Power and thrust are proportional to each other, and the proportionality constant is exhaust velocity. THAT'S why I said power.

Power = thrust*exhaustvelocity

Thanks, that (proportionality) is pretty much what I figured, as you can see from my post. However, now I'm curious as to the power ratings of the thrusters that you mentioned. Is that the power output of the thruster, using the equation you gave? Or is it the electrical power input required to operate the thruster at the given thrust level? When you stated the thrusters' power levels in watts, I thought it was the latter. Given the context of your reply, it would seem to be the former.

Anyway, the bottom line seems to be that you need ~1 MW of power for every 10 lbf of thrust. Please correct me if my math is wrong, or if I have a bad understanding of the underlying principles.

Thanks again.
Keep in mind that thrust goes up if you reduce Isp. It's super basic physics. You can build an electric thruster that gets 30 pounds of thrust with 1MW if you reduce the Isp. Or really, just use base SI, and you don't have to use any of these "rules of thumb" or "bottom lines." And heck, just use exhaust velocity. I think Isp (in s) will eventually be deprecated.

1MW/(10km/s) = 1,000,000 Watts/(10,000 m/s) = 100 Newtons. Super simple.

Or if you operate at very high exhaust velocity, like 100km/s (10,000s Isp), it's:
10^6 W/(10^5 m/s) = 10 N.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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

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