Author Topic: Proposed Europa Missions  (Read 640942 times)

Offline metaphor

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Re: Proposed Europa Missions
« Reply #380 on: 07/30/2014 03:18 pm »
Sorry for asking a rather basic question but: could the "$1 billion" Europa missions be designed (like Clipper) to take either a VEEGA trajectory after launch on Atlas or a direct trajectory after launch on SLS? Or is there something about $1b that makes that not possible?

Er, this is a weird question. No matter what the cost of the mission, it still has to get to Europa. So it's either going to launch on an Atlas or an SLS. Now some people argue that taking a VEEGA trajectory is going to cost more in operations costs than a direct trajectory, because you have to spend $X per year and it is more years to go that way than directly. So maybe you save $80 million in operating costs with the direct trajectory vs. the VEEGA trajectory (but do you pay more for the launch vehicle?).


Is there also an additional cost due to the thermal insulation needed because of the higher temperatures at Venus?  I seem to remember that being an advantage of a straight-to-Jupiter trajectory.

Offline Blackstar

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Re: Proposed Europa Missions
« Reply #381 on: 07/30/2014 04:44 pm »
Sorry for asking a rather basic question but: could the "$1 billion" Europa missions be designed (like Clipper) to take either a VEEGA trajectory after launch on Atlas or a direct trajectory after launch on SLS? Or is there something about $1b that makes that not possible?

Er, this is a weird question. No matter what the cost of the mission, it still has to get to Europa. So it's either going to launch on an Atlas or an SLS. Now some people argue that taking a VEEGA trajectory is going to cost more in operations costs than a direct trajectory, because you have to spend $X per year and it is more years to go that way than directly. So maybe you save $80 million in operating costs with the direct trajectory vs. the VEEGA trajectory (but do you pay more for the launch vehicle?).


Is there also an additional cost due to the thermal insulation needed because of the higher temperatures at Venus?  I seem to remember that being an advantage of a straight-to-Jupiter trajectory.

I've heard something about that too, but I suspect that it's not a big cost. Really, it's just insulation (plus the engineering evaluation). Shouldn't cost much.

Offline Blackstar

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Re: Proposed Europa Missions
« Reply #382 on: 07/30/2014 04:48 pm »
Europa Clipper Would Wash Out Other Nuclear-powered Missions.

SpaceNews generally writes does very good reporting, and this article is except for one omission.  The Clipper mission can also be done (based on current engineering assessments) with solar panels.  There are various engineering and budget trades (solar panels are heavier and must always point toward the sun; but the solar option is cheaper than the Pu-238 option). 

So far as I know, there's been no decision on which direction to go.

If the Clipper doesn't use Pu-238, then NASA could make MMRTGs available to Discovery and New Horizon missions.  There are a number of concepts that either depend on a plutonium power supply or would benefit from it.


There's also a hybrid solar/RTG option that was going to be evaluated as of a few months ago. But RTGs are the lowest risk option. I suspect that for an expensive mission they will want the lowest risk option.

Offline baldusi

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Re: Proposed Europa Missions
« Reply #383 on: 07/30/2014 05:50 pm »
Europa Clipper Would Wash Out Other Nuclear-powered Missions.

SpaceNews generally writes does very good reporting, and this article is except for one omission.  The Clipper mission can also be done (based on current engineering assessments) with solar panels.  There are various engineering and budget trades (solar panels are heavier and must always point toward the sun; but the solar option is cheaper than the Pu-238 option). 

So far as I know, there's been no decision on which direction to go.

If the Clipper doesn't use Pu-238, then NASA could make MMRTGs available to Discovery and New Horizon missions.  There are a number of concepts that either depend on a plutonium power supply or would benefit from it.


There's also a hybrid solar/RTG option that was going to be evaluated as of a few months ago. But RTGs are the lowest risk option. I suspect that for an expensive mission they will want the lowest risk option.
If they go with SLS, RTG also mean nuclear-rating it.

Offline Blackstar

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Re: Proposed Europa Missions
« Reply #384 on: 07/30/2014 06:13 pm »
If they go with SLS, RTG also mean nuclear-rating it.

Yes. But I think that's something that is going to have to happen eventually. If you assume that SLS will become operational and that it will be used for decades to launch human missions, then it will eventually carry RTGs for human missions.

So I think the most important/relevant question is who pays for that nuclear certification: the science community or the human spaceflight community?

Offline a_langwich

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Re: Proposed Europa Missions
« Reply #385 on: 07/30/2014 06:49 pm »
Europa Clipper Would Wash Out Other Nuclear-powered Missions.

SpaceNews generally writes does very good reporting, and this article is except for one omission.  The Clipper mission can also be done (based on current engineering assessments) with solar panels.  There are various engineering and budget trades (solar panels are heavier and must always point toward the sun; but the solar option is cheaper than the Pu-238 option). 

So far as I know, there's been no decision on which direction to go.

If the Clipper doesn't use Pu-238, then NASA could make MMRTGs available to Discovery and New Horizon missions.  There are a number of concepts that either depend on a plutonium power supply or would benefit from it.


There's also a hybrid solar/RTG option that was going to be evaluated as of a few months ago. But RTGs are the lowest risk option. I suspect that for an expensive mission they will want the lowest risk option.

I would think the hybrid option would be pretty competitive on risk.  You can get just enough RTGs to support a baseline science level, so that even if the solar completely disappeared you could get most of the science done.  And, truth is, solar panels aren't too shabby in reliability themselves.  If solar panels are safe enough to risk for the $8 billion JWSC and Hubble, they are probably okay for a measly $1 - $2 billion mission.

But the hybrid option would carry all the complication, cost, size, and weight of both the RTGs and solar and then some.  Maybe not a problem if you are launching on SLS and you don't have the money to fill the size/weight envelope with instruments, but could be trouble for an Atlas.  Still, it might be worth it, IF it enables another small mission or two to take place (meaning there is some assurance the RTG capability wouldn't just sit unused for the entire time frame).

It will be interesting, once Falcon Heavy gets going, to see what its payload/C3 graph looks like. 

Offline Jim

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Re: Proposed Europa Missions
« Reply #386 on: 07/30/2014 07:02 pm »
  If solar panels are safe enough to risk for the $8 billion JWSC and Hubble, they are probably okay for a measly $1 - $2 billion mission.


Not the same trade.  The issue is getting enough power which does not apply to JWST and HST and not reliability.
The risk for Europa is holding to a spacecraft power level and then having the mass for large enough panels with margin to supply the required levels.

Europa needs more power than other probes because of the radar mapper.
« Last Edit: 07/30/2014 07:03 pm by Jim »

Offline Blackstar

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Re: Proposed Europa Missions
« Reply #387 on: 07/30/2014 07:02 pm »
I would think the hybrid option would be pretty competitive on risk.  You can get just enough RTGs to support a baseline science level, so that even if the solar completely disappeared you could get most of the science done.  And, truth is, solar panels aren't too shabby in reliability themselves.  If solar panels are safe enough to risk for the $8 billion JWSC and Hubble, they are probably okay for a measly $1 - $2 billion mission.

But the hybrid option would carry all the complication, cost, size, and weight of both the RTGs and solar and then some.  Maybe not a problem if you are launching on SLS and you don't have the money to fill the size/weight envelope with instruments, but could be trouble for an Atlas.  Still, it might be worth it, IF it enables another small mission or two to take place (meaning there is some assurance the RTG capability wouldn't just sit unused for the entire time frame).

It will be interesting, once Falcon Heavy gets going, to see what its payload/C3 graph looks like. 

I don't think they would count risk in this case as "solar plus RTG." Instead, the risk comes in integrating those two technologies. That might seem easy to us, who don't know anything about doing it, but I would note that it has not been done before. There could be all kinds of complications that come from running two different power supplies into the bus.

My impression, and I've said this before, is that if you put 100 Europa scientists into a room and told them they could vote for either Atlas or SLS, you would probably get 99 people voting for Atlas. SLS comes with all kinds of unknown and murky political and budgetary risks. Better to go with the known quantity, which is Atlas. So I think that the hybrid RTG/solar option is being evaluated for Atlas, because that's what most of the Europa scientists and engineers believe is the most likely launch vehicle.
« Last Edit: 07/30/2014 07:20 pm by Blackstar »

Offline metaphor

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Re: Proposed Europa Missions
« Reply #388 on: 07/30/2014 08:28 pm »

It will be interesting, once Falcon Heavy gets going, to see what its payload/C3 graph looks like.

Extrapolating from the 21.2 tons to GTO and 13.2 tons to Mars on the SpaceX website, and the second stage stats here, the Falcon Heavy would only be able to take about 1-2 tons on a trajectory straight to Jupiter.  Adding a solid upper booster stage like a Star 48 would increase the payload to about 3-4 tons.  The payload would go up to 13-14 tons using a VEEGA.

Offline denis

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Re: Proposed Europa Missions
« Reply #389 on: 07/30/2014 11:58 pm »
Sorry for asking a rather basic question but: could the "$1 billion" Europa missions be designed (like Clipper) to take either a VEEGA trajectory after launch on Atlas or a direct trajectory after launch on SLS? Or is there something about $1b that makes that not possible?

Er, this is a weird question. No matter what the cost of the mission, it still has to get to Europa. So it's either going to launch on an Atlas or an SLS. Now some people argue that taking a VEEGA trajectory is going to cost more in operations costs than a direct trajectory, because you have to spend $X per year and it is more years to go that way than directly. So maybe you save $80 million in operating costs with the direct trajectory vs. the VEEGA trajectory (but do you pay more for the launch vehicle?).


Is there also an additional cost due to the thermal insulation needed because of the higher temperatures at Venus?  I seem to remember that being an advantage of a straight-to-Jupiter trajectory.

I've heard something about that too, but I suspect that it's not a big cost. Really, it's just insulation (plus the engineering evaluation). Shouldn't cost much.
That's a pretty wild statement. How do you know it would just need "extra insulation" ? It depends a lot on the spacecraft design. Maybe it's just insulation? Maybe it will need a new attitude "BBQ-like" mode? Maybe it will need active thermal control?

As for the cost of engineering evaluation, it is one of the main reason all these missions cost billions.

« Last Edit: 07/31/2014 12:09 am by denis »

Offline denis

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Re: Proposed Europa Missions
« Reply #390 on: 07/31/2014 12:03 am »

If they go with SLS, RTG also mean nuclear-rating it.

What does nuclear-rating a launcher mean ?

I thought the RTG were designed to survive intact even an explosion of the launcher.  Isn't it the case ?

Offline Blackstar

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Re: Proposed Europa Missions
« Reply #391 on: 07/31/2014 02:30 am »
Sorry for asking a rather basic question but: could the "$1 billion" Europa missions be designed (like Clipper) to take either a VEEGA trajectory after launch on Atlas or a direct trajectory after launch on SLS? Or is there something about $1b that makes that not possible?

Er, this is a weird question. No matter what the cost of the mission, it still has to get to Europa. So it's either going to launch on an Atlas or an SLS. Now some people argue that taking a VEEGA trajectory is going to cost more in operations costs than a direct trajectory, because you have to spend $X per year and it is more years to go that way than directly. So maybe you save $80 million in operating costs with the direct trajectory vs. the VEEGA trajectory (but do you pay more for the launch vehicle?).


Is there also an additional cost due to the thermal insulation needed because of the higher temperatures at Venus?  I seem to remember that being an advantage of a straight-to-Jupiter trajectory.

I've heard something about that too, but I suspect that it's not a big cost. Really, it's just insulation (plus the engineering evaluation). Shouldn't cost much.
That's a pretty wild statement. How do you know it would just need "extra insulation" ? It depends a lot on the spacecraft design. Maybe it's just insulation? Maybe it will need a new attitude "BBQ-like" mode? Maybe it will need active thermal control?

As for the cost of engineering evaluation, it is one of the main reason all these missions cost billions.



Please, tell me some more. I don't know much about this subject.

Offline sdsds

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Re: Proposed Europa Missions
« Reply #392 on: 07/31/2014 03:22 am »
if you put 100 Europa scientists into a room and told them they could vote for either Atlas or SLS, you would probably get 99 people voting for Atlas.

I understand why today's researchers are the population one would first think to poll. For them, now, arrival dates in 2025 and 2028 don't look that far apart. Nor do departure dates in 2022 and 2021. But as the departure dates get closer the calculus might change. Engineers might want those extra few months of time to assure the spacecraft is ready. And a student in 2021 is going to see a meaningful difference between a 2025 arrival and a 2028 arrival.

In any case, the notion that a mission in development can "maintain dual launch capability through CDR" seems in the current political reality to mandate that it do so.
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Offline Blackstar

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Re: Proposed Europa Missions
« Reply #393 on: 07/31/2014 01:23 pm »
I understand why today's researchers are the population one would first think to poll.

Yeah, because they're the only ones that actually have the knowledge and expertise.

Offline a_langwich

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Re: Proposed Europa Missions
« Reply #394 on: 07/31/2014 07:38 pm »
I would think the hybrid option would be pretty competitive on risk.  You can get just enough RTGs to support a baseline science level, so that even if the solar completely disappeared you could get most of the science done.  And, truth is, solar panels aren't too shabby in reliability themselves.  If solar panels are safe enough to risk for the $8 billion JWSC and Hubble, they are probably okay for a measly $1 - $2 billion mission.

But the hybrid option would carry all the complication, cost, size, and weight of both the RTGs and solar and then some.  Maybe not a problem if you are launching on SLS and you don't have the money to fill the size/weight envelope with instruments, but could be trouble for an Atlas.  Still, it might be worth it, IF it enables another small mission or two to take place (meaning there is some assurance the RTG capability wouldn't just sit unused for the entire time frame).

It will be interesting, once Falcon Heavy gets going, to see what its payload/C3 graph looks like. 

I don't think they would count risk in this case as "solar plus RTG." Instead, the risk comes in integrating those two technologies. That might seem easy to us, who don't know anything about doing it, but I would note that it has not been done before. There could be all kinds of complications that come from running two different power supplies into the bus.

My impression, and I've said this before, is that if you put 100 Europa scientists into a room and told them they could vote for either Atlas or SLS, you would probably get 99 people voting for Atlas. SLS comes with all kinds of unknown and murky political and budgetary risks. Better to go with the known quantity, which is Atlas. So I think that the hybrid RTG/solar option is being evaluated for Atlas, because that's what most of the Europa scientists and engineers believe is the most likely launch vehicle.


Re: Atlas vs SLS, seems pretty reasonable to me.  ANY never-flown rocket would of course be riskier, and the large size and development cost and schedule of SLS, and the fickleness of using a manned rocket for an unmanned mission and depending essentially on the manned program for that impetus--yes, it's more risky.

Re: combining solar and RTGs, having built voltage converters and power management buses, I think combining them would be fairly easy.  AFAIK there will still be a layer of voltage conversion to the bus voltage chosen for instruments; the input to that voltage conversion usually has a wide latitude/tolerance for different sources and voltages.  Especially for a solar panel system, the combination would be simple.  The RTG would just look like another battery, permanently charged.  It IS just another battery.

I don't know how feasible or practical solar power by itself is; I guess Juno will retire a lot of that risk when it starts returning science?  But Juno's panels were 340 kg...that's a pretty big chunk out of a probe's weight budget, isn't it?  That doesn't include the batteries.  340 kg for 420 W (EOM)...a little more than 2 MMRTGs, right?  To me, that's the trade, along with the difficulties of stowing/unfurling, figuring out how to point your probe at the target while your arrays point toward the sun and try to maximize insolation, arranging your instruments and comm to avoid being blocked by the panels, etc. 

Online vjkane

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Re: Proposed Europa Missions
« Reply #395 on: 07/31/2014 08:17 pm »
Another issue with solar is that much of the power goes to running heaters in the spacecraft (about 50% in the case of Juno if memory serves me right). Mmrtg's have heat to spare

Offline a_langwich

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Re: Proposed Europa Missions
« Reply #396 on: 07/31/2014 08:22 pm »
But as the departure dates get closer the calculus might change.

Well, sure, because "future risk" is being retired.  By 2021, if all goes well, SLS will have flights under its belt.  There will presumably be much lower risk that it could get cancelled between mission selection and mission launch.  A lot more people would bet on the high-wire artist after, or even 2/3 of the way through, his walk over the {landmark of interest}.

At the same time, if we are prognosticating the future, I'd bet 99 out of 100 Europa scientists would pick Falcon Heavy in 2021 over SLS.  Possibly even if it still has crappy high-energy mission performance.

In any case, the notion that a mission in development can "maintain dual launch capability through CDR" seems in the current political reality to mandate that it do so.

This may not be so hard for the Clipper concepts, if the mass launched by SLS direct is similar to Atlas VEEGA mass.  The Venus environment should be trivially easy to handle with shading and minor thermal design, since the probe isn't trying to do any science there.

The problem with using SLS for a $1 billion probe is that to halve the price of the budget, you are going to have to throw out instruments, which will reduce both weight and power.  That won't make any significant difference in travel time, either direct or VEEGA, but it means you will be seriously underusing SLS.  And it won't help SLS for people to be talking about cutting half of a $2 billion probe's cost in tight budget times, while flying it on an LV which has cost tens of billions.


Offline Blackstar

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Re: Proposed Europa Missions
« Reply #397 on: 08/01/2014 04:02 pm »
But as the departure dates get closer the calculus might change.

Well, sure, because "future risk" is being retired.  By 2021, if all goes well, SLS will have flights under its belt.


But that's not really it. It's not the danger that SLS will get canceled between now and then, it's all the programmatic instability that would come with using an SLS instead of an Atlas V. Simply put, if the Science Mission Directorate buys an Atlas V for a Europa mission, then they own it. It's theirs. Everybody knows that. But if they go with an SLS, the program managers are always going to be worried that they are at risk from larger political and bureaucratic forces. For instance, if HEOMD decides to change their bookkeeping for SLS and unexpectedly shifts more costs onto the payload side. If I was a Europa scientist, I would want the launch vehicle that is a 100% known variable and where I'm the full owner. There won't be any surprises.
« Last Edit: 08/01/2014 04:03 pm by Blackstar »

Offline baldusi

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Re: Proposed Europa Missions
« Reply #398 on: 08/01/2014 04:07 pm »
There's no internal equivalent to an insurance or warranty?

Offline Blackstar

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Re: Proposed Europa Missions
« Reply #399 on: 08/01/2014 06:11 pm »
There's no internal equivalent to an insurance or warranty?

We're talking about a bureaucracy here. If somebody from the government promised you something would you believe them?

I will pose a theoretical example: suppose when HEOMD and the Science Mission Directorate (SMD) are negotiating over using SLS for the Europa mission HEOMD says that they (HEOMD) will pay the cost of nuclear rating the SLS. Suppose that they say this because they expect that in a few years they are going to have to nuclear rate the SLS for HEOMD missions. So SMD says yes. And then a few years later, HEOMD slips its plans and no longer plans to fly its own nuclear payloads on SLS in the next few years. And so, because they do not need to nuclear rate SLS for their own purposes, they say "SMD, you are the only user who needs the nuclear capability, so you should pay for nuclear rating the SLS." And then SMD gets stuck with an added cost that they were told that they would not have to pay. Surprise!

I am not saying that this is the kind of thing that will happen. What I am saying is that it is the kind of thing that can happen. And people know it.*

So when a program selects a launch vehicle, or anything else, they try to maximize the things that they can control within their own office, and minimize the things that other people control. If I was a Europa scientist, I would want to use the rocket that has a high flight rate, high reliability rate, and that my people have a lot of experience with.







*I am sure that if you talked to principal investigators who ran missions in the past you could get lots of similar horror stories. I remember New Horizons PI Alan Stern explaining once about how after his mission was selected his team wanted to pick a launch vehicle and start designing their spacecraft for that vehicle. However, because of some contracting policy issue at NASA, NASA told New Horizons that they could not pick a single launch vehicle at that time. That forced New Horizons to design for both Atlas and Delta for much of their development, which Stern claimed cost them a lot of money in the design phase. Eventually, NASA picked an Atlas. My point is that these are the kinds of decisions that program managers like to nail down quickly, and they want to go with the safest and most well-known choice. They do not necessarily want the highest performance option. Thus, even when Falcon Heavy starts flying, I suspect it will take a long time before program managers will embrace it. They will all want to see a lot of successful flights before they agree to use it. "Cheap" is not really cheap if the launch vehicle fails.

 

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