Manned mission to Ceres

[Star One]

Assuming we finally made it to Mars how much more difficult would it be to achieve a manned mission to Ceres? Would the most effective way be to actually launch a mission from Mars itself rather than the Earth.

[NovaSilisko]

Assuming we finally made it to Mars how much more difficult would it be to achieve a manned mission to Ceres? Would the most effective way be to actually launch a mission from Mars itself rather than the Earth.

The inclination of Ceres is a huge problem. One way to overcome that that comes to mind is a gravity assist via Mars, but that's a rare alignment of objects. Radiation is an issue, both due to trip times and owing to Ceres' almost complete lack of atmosphere. The amount of water ice could be useful to manufacture propellant for returning, perhaps.

[Star One]

Assuming we finally made it to Mars how much more difficult would it be to achieve a manned mission to Ceres? Would the most effective way be to actually launch a mission from Mars itself rather than the Earth.

The inclination of Ceres is a huge problem. One way to overcome that that comes to mind is a gravity assist via Mars, but that's a rare alignment of objects. Radiation is an issue, both due to trip times and owing to Ceres' almost complete lack of atmosphere. The amount of water ice could be useful to manufacture propellant for returning, perhaps.

Is it actually harder to reach Ceres than some of the moons of Jupiter then?

[Robotbeat]

Assuming we finally made it to Mars how much more difficult would it be to achieve a manned mission to Ceres? Would the most effective way be to actually launch a mission from Mars itself rather than the Earth.

The inclination of Ceres is a huge problem. One way to overcome that that comes to mind is a gravity assist via Mars, but that's a rare alignment of objects. Radiation is an issue, both due to trip times and owing to Ceres' almost complete lack of atmosphere. The amount of water ice could be useful to manufacture propellant for returning, perhaps.

Is it actually harder to reach Ceres than some of the moons of Jupiter then?

Not if you're using solar-electric propulsion, like was used to reach Ceres in the first place and is currently the favorite for Mars missions.

[Nilof]

Assuming we finally made it to Mars how much more difficult would it be to achieve a manned mission to Ceres? Would the most effective way be to actually launch a mission from Mars itself rather than the Earth.

The inclination of Ceres is a huge problem. One way to overcome that that comes to mind is a gravity assist via Mars, but that's a rare alignment of objects. Radiation is an issue, both due to trip times and owing to Ceres' almost complete lack of atmosphere. The amount of water ice could be useful to manufacture propellant for returning, perhaps.

Is it actually harder to reach Ceres than to reach some of the moons of Jupiter then?

In terms of impulsive delta-v? Yes, definitely. Capturing into the sphere of influence of a gas giant is very easy because of the Oberth effect, and at that point you can use gravity assists from the very massive moons to slow down from the capture orbit.

However, Jupiter is noticeably more difficult in terms of travel time, lack of solar power, and radiation belts. Furthermore, with solar electric propulsion the delta-v to Ceres is very achievable making Ceres the easier target in practice.

[Nomadd]

Assuming we finally made it to Mars how much more difficult would it be to achieve a manned mission to Ceres? Would the most effective way be to actually launch a mission from Mars itself rather than the Earth.

The inclination of Ceres is a huge problem. One way to overcome that that comes to mind is a gravity assist via Mars, but that's a rare alignment of objects. Radiation is an issue, both due to trip times and owing to Ceres' almost complete lack of atmosphere. The amount of water ice could be useful to manufacture propellant for returning, perhaps.

Is it actually harder to reach Ceres than some of the moons of Jupiter then?

Not if you're using solar-electric propulsion, like was used to reach Ceres in the first place and is currently the favorite for Mars missions.

Considering the much higher thrust to weight you'd need since it's hard to put people to sleep for several years at a time during the mission, and the much, much higher mass of the mission in the first place for manned, I'm not sure solar would fly. Nuclear electric maybe.

[Archibald]

Two older threads 

http://forum.nasaspaceflight.com/index.php?topic=25463.msg754248#msg754248

http://forum.nasaspaceflight.com/index.php?topic=18832.msg480329#msg480329

[Robotbeat]

Assuming we finally made it to Mars how much more difficult would it be to achieve a manned mission to Ceres? Would the most effective way be to actually launch a mission from Mars itself rather than the Earth.

The inclination of Ceres is a huge problem. One way to overcome that that comes to mind is a gravity assist via Mars, but that's a rare alignment of objects. Radiation is an issue, both due to trip times and owing to Ceres' almost complete lack of atmosphere. The amount of water ice could be useful to manufacture propellant for returning, perhaps.

Is it actually harder to reach Ceres than some of the moons of Jupiter then?

Not if you're using solar-electric propulsion, like was used to reach Ceres in the first place and is currently the favorite for Mars missions.

Considering the much higher thrust to weight you'd need since it's hard to put people to sleep for several years at a time during the mission, and the much, much higher mass of the mission in the first place for manned, I'm not sure solar would fly. Nuclear electric maybe.

Actually, the longer time scale improves the case for solar (cancelling out somewhat the reduced light when you approach Ceres). I would bet that solar-electric still beats out nuclear-electric for mission-average power given the same mass.

Solar would be able to reduce the trip time compared to the equivalent chemical/thermal or nuclear-electric IMLEO.


Why do people automatically think that solar is just an inferior compromise? In most cases, it's markedly superior to other options (including reductions in trip time for the same IMLEO... it's just that often-times it makes sense to trade longer trip times for lower IMLEO).

[Robotbeat]

When you get to outer planets missions, it starts making sense to use both significant hydrogen shielding (targeting GCR) and artificial gravity. (Although really, we'll be better off if we can address especially the former using drugs and other medical treatments.) Not sure if a Ceres mission needs those, yet. What are the estimated trip times, starting with an impulsive Holmann-like trajectory?

EDIT: Trip times for electric propulsion are around days each way: http://news.nationalgeographic.com/news/2013/11/131118-ceres-asteroid-solar-system-space-science/

[Comga]

Isn't this a bit premature?
Besides having little but Musk's fifteen year bet on getting to Mars, we don't know much about the surface of Ceres, but are learning more every week as Dawn approaches.
Perhaps we can discuss what a person could do on the surface after we get some images of it this summer.
Of course, it's not as premature as discsions of terraforming are in the first post of the linked thread.
http://forum.nasaspaceflight.com/index.php?topic=25463.msg754248#msg754248

edit: Can we keep this about Ceres or does it have to devolve into nuclear vs solar power, etc.?

[Robotbeat]

Here's a study:
http://www.sciencedirect.com/science/article/pii/S0094576513003950
Key points are:
270 day transit each way, total time about 2 years. A supply mission would precede the manned mission. They assumed propulsion system mass of 5kg/kWe (200W/kg). Solar-electric could do that as well (averaged over the mission), if an IKAROS-style lightweight array (using solar sail type booms) were used.

[Robotbeat]

...
edit: Can we keep this about Ceres or does it have to devolve into nuclear vs solar power, etc.?

Unfortunately, that's really the key technology question of the mission. And it's not obvious either way which should be used (ignoring cost) since it's on the border of the inner and the outer solar system.

[Star One]

Here's a study:
http://www.sciencedirect.com/science/article/pii/S0094576513003950
Key points are:
270 day transit each way, total time about 2 years. A supply mission would precede the manned mission. They assumed propulsion system mass of 5kg/kWe (200W/kg). Solar-electric could do that as well (averaged over the mission), if an IKAROS-style lightweight array (using solar sail type booms) were used.

Thanks for that link. As a general point I hadn't realised as much study had gone into manned missions to Ceres as there appears to have been.

[Robotbeat]

Oh, in this field, people have done conceptual studies of anything you could think up, usually multiple times.

Just check out: http://www.sciencedirect.com/science/article/pii/S0094576513003950

[Nomadd]

It's mostly that I get the impression that solar concepts using things like solar sail type booms are being compared to more realistic, or near term nuke ideas when you talk about needing a MW or more. Can't say I've actually got a handle on the temp/area/heat numbers for nuke radiators yet. But, when you get into advanced solar, as in W/KG, you can bet array repairs won't be a guy on a robot arm stitching it together with fishing line.
 Wouldn't be the first time I'm wrong, and there's no one I trust more in this asylum than Robotbeat when it comes to practical ideas and numbers.
 I'll give nuke, solar and electric propulsion another decade to settle out before I start making bets.

[KelvinZero]

edit: Can we keep this about Ceres or does it have to devolve into nuclear vs solar power, etc.?

Im quite interested about operations at the destination itself.

Having gone all that way, and having such low gravity, would it be reasonable to set down at multiple sites? (a google search found a value of about 0.25 km/s to reach orbit from Ceres).. Or maybe you should set down multiple rovers at different sites, begin teleoperating them from earth, but hand over to the human crew as they approach the target. It could give them something to do besides anything else.

About being premature, it would also be interesting to list all the useful things we do not know that we may know in a year (from the Dawn mission)

[Nilof]

edit: Can we keep this about Ceres or does it have to devolve into nuclear vs solar power, etc.?

Im quite interested about operations at the destination itself.

Having gone all that way, and having such low gravity, would it be reasonable to set down at multiple sites? (a google search found a value of about 0.25 km/s to reach orbit from Ceres).. Or maybe you should set down multiple rovers at different sites, begin teleoperating them from earth, but hand over to the human crew as they approach the target. It could give them something to do besides anything else.

About being premature, it would also be interesting to list all the useful things we do not know that we may know in a year (from the Dawn mission)

This makes me curious about the cost of performing suborbital hops on Ceres. The situation should be somewhat different from the moon due to the fast rotation rate, which is enough to provide a sizable faction of orbital velocity at the equator.

[notsorandom]

It looks like a Ceres mission might be pertty doable, roughly as tricky as a Mars mission. I'm wondering about how the missions compare in terms of cost. The missions have a lot in common as much of the hardware could be used for both. They will require lifting roughly the same amount of hardware so launch costs would be comparable. A Mars mission may have more mass due to its lander. Both missions require lengthy stays in deep space. The propulsion will be pretty comparable unless solar can be done for Mars and for some reason not for Ceres.

There are differences though. Ceres requires more Delta V. However landing on Ceres is simpler than Mars, and even the Moon. The lander for Mars is going to be very expensive and I think that if trading the costs of the two missions will contribute to bulk of the difference in cost. Ceres needs more solar panels, propellant and food but the cost of adding those are pretty trivial. Mars has quite a bit more gravity which may be a huge benefit to the crew's health. If we were pretty comfortable with long duration deep space flight Ceres might be cheaper to visit before a mission to the surface of Mars. We are eventually going to want to have humans check out that really bright crashed alien ship on Ceres anyway. 

[simonbp]

Probably the best "lander" on Ceres would have just enough propellant to "hop" around to several different places on the surface collecting samples. Considering probably the highest priority site is also probably covered in water ice, ISRU seems obvious.

Also, speaking from microgravity aircraft experience, Mars still has pretty low gravity, and you still need more effort to move around on the Moon than zero-g, so I'm dubious there would be any substantial health differences based simply on gravity.

[Hop_David]

Not if you're using solar-electric propulsion, like was used to reach Ceres in the first place and is currently the favorite for Mars missions.

Ion engines have very weak thrust. Even on Ceres T/W woul be less than 1. Chemical would be need for ascent from Ceres surface as well as soft landing.

[KelvinZero]

Im not normally a fan, but how about a rotovator?
(edit: just did the math and got 6km radius for a 1g, 0.25km/s system. nah... just landing on rockets where you want and leaving when you want is far more attractive)

Another interesting question is what to use instead of rovers (including robotic rovers). I imagine some sort of bouncing thing. Or maybe just very large but light wheels so that flipping over is not a problem?

Also, how about some sort of reaction wheel for rovers and suits. I realise you can't get angular momentum for free, but the important thing for a suit is that you are helmet-side-up at the instant you return to the surface after a step. Maybe you would also have some sort of cold gas thruster in the occasion that the wheel becomes saturated? Or maybe all you need is a shock absorbing cage around the helmet so you can land on it as often as you like.

How much mass to get a cereanaut back to orbit? Perhaps this could be an option of every suit in addition to the lander?

[Robotbeat]

Not if you're using solar-electric propulsion, like was used to reach Ceres in the first place and is currently the favorite for Mars missions.

Ion engines have very weak thrust. Even on Ceres T/W woul be less than 1. Chemical would be need for ascent from Ceres surface as well as soft landing.

Well, not really chemical. You could, actually, land and/or launch with cold gas or warm gas thrusters. Even a bottle of superheated steam would technically work.

But I agree you're not going to be doing that landing with a 3000s Isp ion thruster. Not happening.

[Nomadd]

Not if you're using solar-electric propulsion, like was used to reach Ceres in the first place and is currently the favorite for Mars missions.

Ion engines have very weak thrust. Even on Ceres T/W woul be less than 1. Chemical would be need for ascent from Ceres surface as well as soft landing.

I was always amazed at the tiny size of the tanks on the lunar ascent module. A plate of beans for dinner the previous night would probably be enough to take off from Ceres.

[MATTBLAK]

With only 2.8% percent of a G on Ceres, it's possible...

[Paul451]

Ion engines have very weak thrust. Even on Ceres T/W woul be less than 1. Chemical would be need for ascent from Ceres surface as well as soft landing.

I think the assumption with Ceres is usually that ISRU once you get there is going to allow simple chemical rockets in the region. SEP/NEP is for long distances.

General aside:
The consensus seems to be that SEP is probably sufficient for a Ceres mission; while Ceres itself is a little far out, most of the acceleration happens inside of Mars' orbit where SEP is more mass-efficient than NEP. However nuclear may be more appropriate than solar for operations at Ceres. In which case, it would make sense saving mass by using the same reactor for your electric-drive on the trip out. You have to carry the thing anyway.

Im not normally a fan, but how about a rotovator? (edit: just did the math and got 6km radius for a 1g, 0.25km/s system. nah...

Why 1g? Humans handle 3-4g during launch easily.

[KelvinZero]

Im not normally a fan, but how about a rotovator? (edit: just did the math and got 6km radius for a 1g, 0.25km/s system. nah...

Why 1g? Humans handle 3-4g during launch easily.

Just an example. You just divide by acceleration so 3g gives about 2km and so on.

I think I would have considered it further if the dimensions were similar to typical artificial gravity spacecraft. There was a big thread saying AG is not needed, but suppose a spinning AG vehicle design happened to trivially solve the landing on Ceres? That turned out not the case, and then on top of that you have all the extra disadvantages such as only landing at equator, and tricky unproven pickup only at very precise points in time. Rockets are just way more practical for exploration.

I can definitely see someone arguing rotovators for trading with a colony there, or something like that.

[Paul451]

(edit: just did the math and got 6km radius for a 1g, 0.25km/s system. nah...

Aside: The thing is, 6km is not that difficult a tether length, 2km even easier. We've already played with similar lengths. (Not well. But... {waves hand} ...it's down to practice and engineering, not materials or fundamental technology.)

all the extra disadvantages such as only landing at equator, and tricky unproven pickup only at very precise points in time.

Meh. We can only launch from Earth from specific locations during certain windows. With a synchronised rotovator (where the tether-spin is in some exact proportion of the circumference, so it "touches" the same set of points) you have the locations for your settlements and "space-ports". Given how easy it is to move around on the surface, those should be sufficient as your entry and exit points.

I can definitely see someone arguing rotovators for trading with a colony there, or something like that.

For cargo trading (launching ice/fuel/air, for example), you also have the option of a horizontal rotating arm on the surface. The stupidly low gravity allows you to build a long rotating arm to throw cargoes into orbit, without the tip velocity (or droop from gravity) exceeding the material limits. The simplest would be a non-rigid tether, of course, but spin-up/down would be harder. You have to winch in and out each time. Winches loves teh vacuum.

In theory, using a long enough non-rigid (winched) cable, you could even launch humans with a horizontal throwing arm. That'd be a fun system to design though.

[Hop_David]

Im not normally a fan, but how about a rotovator?

Ceres is a great place for a Clarke/Artsutanov style space elevator. The small gravity well and high angular velocity make this much less challenging.

Ceres synchronous orbit is 706 km above Ceres' equator. A 1922 km tether would be long enough to maintain tension. There's not much stress on the tether so the taper ratio is 1 even for ordinary materials like Kevlar.

An ion engine could dock with a Ceres elevator. One of my favorite day dreams is lots of xenon dissolved in Ceres' subterranean oceans.

The speed at the top of a 1922 km Ceres elevator would be about .45 km/s. Not enough for injection to a Ceres to Earth transfer orbit but it would help.

A Ceres elevator 15,000 km tall would suffice to hurl a ship down to 1.52 A.U. perihelion, the neighborhood of Phobos and Deimos.

[Robotbeat]

Argon works nearly as well as Xenon.

But there ARE electric thrusters which can operate on water.

[Hop_David]

Argon works nearly as well as Xenon.

But there ARE electric thrusters which can operate on water.

And there may be an abundance of water on Ceres. I'm hoping those white spots are water that has made it to the surface after meteorite impacts punctured the surface.

Besides great ISP, ion engines also seem to have great durability. I had assumed that was due at least in part to using noble gases as the reaction mass. Would an ion engine that uses more chemically active propellent be as long lived?

[Hanelyp]

Would an ion engine that uses more chemically active propellent be as long lived?

Taking "ion engine" to mean the more general class of electric thrusters, that depends on the engine.  Electrodes tend to be a difficulty for longevity.  Some electric thrusters energize the propellant by induction instead.

[KelvinZero]

Meh. We can only launch from Earth from specific locations during certain windows.

Im interested about what that means for Ceres. Would a manned mission there be restricted to certain locations? My google search suggested you need about a 1/3 km/s if you are not exploiting the equator, 0.25km/s at the equator but someone should check that.

I guess i just don't see the Rotovator as an enabling technology for Ceres, I mean it isn't the thing that will make us say "Hey! we can do Ceres!". The only key requirements seem to be SEP, long term lifesupport, and the confidence for really long missions.

What about radiation? Mars durations seem ok from discussions here though apparently not within NASA guidelines.

[Robotbeat]

By the way, electromagnetic launch sleds, like are used in the newer supercarriers, can get about 100m/s in operation. You may be able to improve that to 200m/s, then you just need another 70m/s or so to circularize the orbit (assuming you're launching from the equator, which gives you about 90-100m/s advantage).

[Paul451]

I guess i just don't see the Rotovator as an enabling technology for Ceres, I mean it isn't the thing that will make us say "Hey! we can do Ceres!".

It's not really an enabler for a first manned mission. I think it was proposed more as a long term thing. (Ie, "what if a Ceres settlement is trading with other settlements?")

However, a 5-10km tethers really aren't that bad, technologically speaking. It might be a way of landing robotic explorers without needing chemical rockets. That means you can do a bunch of Curiosity-Class robotic landers with just SEP. (Too early to trust a 2-years-in-vacuum tether and winch to work reliably enough for a manned mission. But you could probably say the same about any chemical-rocket lander.)

The only key requirements seem to be SEP, long term lifesupport, and the confidence for really long missions.

It would be nice to have some data about the availability and nature of the ice. Allowing you to pre-send ISRU infrastructure. (Hopefully Dawn, soon. But I suspect more detail will be required.) That makes your mission a little easier if you know you can get at least water and air when you arrive. Even better water, air, and fuel.

[A_M_Swallow]

Not if you're using solar-electric propulsion, like was used to reach Ceres in the first place and is currently the favorite for Mars missions.

Ion engines have very weak thrust. Even on Ceres T/W woul be less than 1. Chemical would be need for ascent from Ceres surface as well as soft landing.

With a bit of thought the chemical thrusters can form part of the RCS. Choosing the right thruster will permit a 5 second burn to get the spacecraft to orbit.

[AlanSE]

I will try to do somewhat of an objective comparison between a GEO tether and chemical propulsion for landing on Ceres. I will assume the equator.

Chemical

Let's assume propellant ejection velocity of 3,000 km/s to be realistic. The equator of Ceres is spinning at roughly 95.5 m/s. The orbital velocity at the surface is 360 m/s, making for a difference of 264.5 m/s neglecting gravity drag. That should be pretty small anyway since the gravity is so little. We could presumably use solar-electric or nuclear-electric ion drives to get to orbit to begin with.

Mass ratio comes out to a ballpark of around exp(-264.5/3000) = 0.9156, meaning that the mass of propellant to payload as a ratio is about 0.092

GEO Tether

Yes, we can assume a taper ratio of 1, but that doesn't mean the tether is massless. The longer the span is, and the higher the tension is, the heavier the tether will be. I will denote specific strength by "sigma".

M_tether = M_payload g L / sigma
(M_tether/M_payload) = (1922 km)*(0.025*9.8 m/s^2)/(2514e3 m^2/s^2) = 0.1873

/end comparison

Interestingly, the mass penalty would be almost the same for both options if the chemical rocket both sets down and lifts back up. If you assumed in-situ resource use for the trip back up then clearly rockets will win for this particular comparison. But that's not very fair.

Obviously the rotovator would perform vastly better (because of shorter length), but if you spun up with propellant in the first place you'll defeat the entire point. In fact, the only way I can see this making sense is if you're already using the tether for artificial gravity. Honestly, that's a bit larger than what would normally be practical for artificial gravity. Too much risk to dangle on a several-km tether for many years. There might be propellant-less ways to spin up the tether as you get close to Ceres, but I don't know what these would be. Actually, you could use a slender 1,000 km tether to make direct contact with the dwarf planet while your craft is in GEO. Then you could use this anchor to slowly spin up your rotovator. You still have all kinds of wonky problems with firing an ion engine at the fulcrum of a rotating structure to lower orbit, but as an academic argument it certainly shows that direct momentum exchange activities are viable if you plan to be spending much time or doing enough operations there to make it worth the time.

[Nilof]

Hmm, what about battery-powered low-isp electrothermal thrusters? Normally these are not practical because they have a maximum mass ratio which is too low for most applications, but in this case, they might be a practical option for a hopper using local water as propellant.

[KelvinZero]

It's not really an enabler for a first manned mission. I think it was proposed more as a long term thing. (Ie, "what if a Ceres settlement is trading with other settlements?")

Fair enough. I was just looking at "suppose we wanted to go now"

Longer term, I like the idea of a magrail on the equator. It not only provides access to the rest of the solar system but also local transport and sharing of solar power between day and night. Even more extravagantly, I think all these dwarf planets will become ocean worlds under protective eggshells of ice once we have human industry buried there producing waste heat. There is a bit of math to back that up. It wouldn't take extravagant power levels.

Initially I was wondering why this thread was in advanced concepts but I think there is one good reason: there are moon firsters, mars firsters and asteroid/ARM firsters. No one is seriously proposing Ceres first so this is just a fun academic exercise unless we spot a monolith there or something. If we ever go to Ceres we will already have another world under our belt. We probably won't even think of it as a manned mission in the apollo sense but as extending our domain.

[Nilof]

Initially I was wondering why this thread was in advanced concepts but I think there is one good reason: there are moon firsters, mars firsters and asteroid/ARM firsters. No one is seriously proposing Ceres first so this is just a fun academic exercise unless we spot a monolith there or something. If we ever go to Ceres we will already have another world under our belt. We probably won't even think of it as a manned mission in the apollo sense but as extending our domain.

I think this is mostly because Ceres is the hipster planet that few people actually know about. Up to now we didn't even have any sharp pictures of it. No spacecraft we could build could reach it at a reasonable expense. We are still speculating on its geology.

Dawn has indeed changed the equation noticeably, and Ceres definitely looks much more reachable. Though certainly not easier than Phobos or Deimos.

Longer term, I like the idea of a magrail on the equator. It not only provides access to the rest of the solar system but also local transport and sharing of solar power between day and night. Even more extravagantly, I think all these dwarf planets will become ocean worlds under protective eggshells of ice once we have human industry buried there producing waste heat. There is a bit of math to back that up. It wouldn't take extravagant power levels.

Ceres is indeed a very fun world to think about colonizing. The centigravity environment makes it rather unique. I imagine that colonies there would have some rather interesting architecture. The gravity is just barely low enough that having a dedicated floor in a room may or may not make sense in all situations.

[Stormbringer]

Happily: Ceres is due for a promotion and so is Pluto:

http://blogs.discovermagazine.com/crux/2015/02/25/pluto-ceres-planet-again/#.VPXHIOGoPcQ

[the_other_Doug]

And reading the comments on that article, I'm reminded as to why we want to avoid getting into that topic here...

[Paul451]

If we ever go to Ceres we will already have another world under our belt. We probably won't even think of it as a manned mission in the apollo sense but as extending our domain.

I made a similar comment recently on another site, Ceres will be part of the secondary expansion of human space settlement, not part of early asteroid mining nor an especially early settlement. It's not necessary until humans have spread much further, and not profitable until its necessary.

But thinking about it, there will almost certainly be a manned mission, flags'n'footprints, before settlement expands that far. Once the cost of LEO HSF allows the cost of BEO HSF to drop sharply, I think we'll see a sudden burst of "First!" manned missions. Whether government funded or not. If the cost of BEO drops enough for Musk to send colonists to Mars, then the technology exists for privately funded (or semi-private university-funded) expeditions to other interesting places. Ie, even when "government funded", it won't necessarily be as "the space program". (And that, IMO, will be a very cool thing.)

Eg, buy a MCT that Musk is retiring/replacing due to age. Add a greenhouse module to the MCT built from a second-hand, third-generation Bigelow module. Add a larger SEP, or extra fuel tanks. Buy an old Dragon v2 for a lander (capable of about 450m/s delta-v, bit of tank-modding might bring that up to the necessary 500+m/s). Add your crew and researchers and off you go. Publish or Perish.

Even more extravagantly, I think all these dwarf planets will become ocean worlds under protective eggshells of ice once we have human industry buried there producing waste heat.

Buoyancy is (mostly) independent of gravity, so any structure able to float in water on Earth will be buoyant on Ceres. Pressure, however, does vary with gravity, so the pressure a few hundred metres below the surface of Ceres is no more than a few metres underwater on Earth.

Buoyancy without pressure should allow some extreme structures on Ceres. Stuff you'd never get on Earth without SF technology. Whole cities upside-down against the ice. (Any buoyant structure will eventually melt-float to the surface, so you'd need walls around the top of the structure to trap enough ice and water above the structure to stop it from rising further, assuming you use the ice/water to protect from radiation/etc.)

I think this is mostly because Ceres is the hipster planet that few people actually know about. [...] Dawn has indeed changed the equation noticeably,

It's certainly getting a fair bit of attention now, much more than I saw for the Vesta encounter. (I wonder how much being able to put "dwarf planet Ceres" (sorry Doug) in the headline has helped media coverage outside the usual pop-science mags.)

[Paul451]

Longer term, I like the idea of a magrail on the equator. It not only provides access to the rest of the solar system but also local transport and sharing of solar power between day and night.

At just 1g acceleration, you reach orbital velocity in about 3km, escape velocity in 5km. So you don't need much track to be useful. Interestingly, because there's no atmosphere, a longer track (around 20-30km) would allow you to land too. Approach is only 3 times your typical runway approach, there's no weather, wind or turbulence (barring a few well mapped masscons). You'd only need a few tens of m/s delta-v from your RCS to land on a moving maglev platform; and if you focus on lining up on the track, the maglev platform can worry about staying underneath you.

(The necessary velocity is about double the record speed for a maglev on Earth, however with less than 3% surface gravity, very little energy is wasted on the actual levitation part. However, more than escape velocity is probably exceeding current generation maglev; you'll still need your water-fuelled SEP for the long burn.)

[A_M_Swallow]

No atmosphere means that the maglev can go faster because it is not fighting air resistance.

[Paul451]

No atmosphere means that the maglev can go faster because it is not fighting air resistance.

Not just air resistance. Above a certain speed, the electromagnetic system required for lift starts to add magnetic drag. That still puts a hard limit on maglev, even in vacuum. But reduce the lift required to below 3% and you get vastly less resistance, so can have a higher top speed. Hence I doubt launch- or even escape-velocity would be an issue.

Even just by spacing the physical elements out.
(__ _  _   _    _      _         _              _              _         _      _    _   _  _ _ __)

But the many km/s for Earth-return may be a bridge too far. Being above orbital velocity at surface radius means you need a reverse-lift system to hold the vehicle down at 4-7km/s (or whatever is required for Earth-transfer), that then becomes a drag. (At 7km/s around the equator, you are pulling negative 10g's.)

[edit: Hey, lame ascii diagrams work here. Cool.]

[edit2: I think I'm wrong. I just reread what I'd previously read on this, magnetic drag is proportional to gravity, but it's inversely proportional to velocity. Faster is better, and eventually magnetic-drag plateaus at the gravitational-drag amount. (Misremembered "magnetic drag becomes dominate in a vacuum", (because duh, no aerodynamic drag when there's no aero) as "even in a vacuum, magnetic drag becomes dominant at [this speed]".) This doesn't change my last paragraph, 10g's gives you 10 times the gravitational magnetic-drag as an Earth maglev, and hundreds of times that of orbital-velocity on Ceres.]

[Lampyridae]

Why even have a maglev? Put the electromagnets in the ship and use them to grapple the iron strip.

Heck, just have magnetic loops like the lunar coilgun slings of the O'Neill dreams.

[KristianAndresen]

Paul451, do you have any papers that can back up this talk of hard limits on maglev speeds, which deal with general theoretical limitations rather than looking at the drag of specific maglev implementations?

The idea that a 10 fold increase in acceleration necessarily implies a 10 fold increase in drag is not convincing, considering that a simple system of a charged particle being accelerated by moving through a magnetic field does not have any drag, regardless of speed. No work is done on or by the particle since acceleration is perpendicular to the motion.

[AlanSE]

Paul451, do you have any papers that can back up this talk of hard limits on maglev speeds, which deal with general theoretical limitations rather than looking at the drag of specific maglev implementations?

The idea that a 10 fold increase in acceleration necessarily implies a 10 fold increase in drag is not convincing, considering that a simple system of a charged particle being accelerated by moving through a magnetic field does not have any drag, regardless of speed. No work is done on or by the particle since acceleration is perpendicular to the motion.

Maglev should not be compared to charged particle acceleration. The force transmittal is only by magnetic fields from objects with essentially neutral charge. This makes the topology of the problems much nastier. You're accelerating a shaped electromagnet, not a charged mass.

Scaling problems with maglev can be nasty, but I think the way you framed makes this relatively straightforward. If we're keeping all sizes the same, velocities the same, and the payload's magnetic field the same, then the forces will be proportional to the currents in the stationary coils on the surface. I would also assume that the mass of the coils increase proportionally. The heat dissipation also does the same. As such, I would tentatively agree with the assertion that 10x increase in a design's acceleration will correspond with a 10x increase in the track's mass and a 10x increase in the energy it requires.

[Paul451]

Paul451, do you have any papers that can back up this talk of hard limits on maglev speeds

See my edit at the bottom of my post.

"I think I'm wrong. [...] magnetic drag is proportional to gravity, but it's inversely proportional to velocity. Faster is better, and eventually magnetic-drag plateaus at the gravitational-drag amount." - which on Ceres is trivial. I remembered it the other way around, that mag-drag was directly proportional to velocity.

As to why it's different to charged particles, it's because the levitating vehicle has magnetic coils in which a current is induced as it passes through each field on the track. That creates a countering magnetic field and creates resistance. (I think superconductors reduce or eliminate this. And that may be an option on Ceres.)

[Nilof]

I'm not sure if I follow the conversation. If we're talking about acceleration, there are mass driver designs that work for much higher delta-v's. If we're looking at deceleration, you'd need maneuvering thrusters anyway to do the approach properly. In that case, you can certainly use these to maintain altitude while being decelerated.

At three gee of deceleration(feasible for a magnet going through a conducting tube), decelerating from orbit takes ~ten seconds. I don't think maintaining altitude during ten seconds in a centigee environment is a big deal, really.

[Moe Grills]

  Forget Maglev.
Ceres is loaded with H20. Nuclear or solar energy can break down Cerean water into abundant hydrogen and oxygen for propellant. The minor planet would be an excellent fuel-stop for interplanetary expeditions.
There are other obvious bonuses: Low gravity and small escape-velocity means (as an example) you can launch a metric ton of mass from the surface to depart that world using a fraction of that mass in the form of LOX/LH2 propellant.
 An orbiting way-station circling Ceres can serve as a depot for mother ships ready to return to Earth or head out towards the gas giants.
Sunlight on Ceres is stronger than in the jovian system, so solar-power won't be despised.
The surface gravity on Ceres is strong enough for astronauts to feel comfortable; and irony of ironies, you can grow food in greenhouses there.

[KelvinZero]

(this is more colonisation of Ceres than manned mission but never mind)

I plugged some numbers in and as it happens the solar power falling on Ceres is slightly more than the power required to keep Ceres entirely liquid beneath a layer of 1km of ice. The trick would be to somehow direct this solar heat at least 1km underground with some sort of light pipes so that the heat is trapped under a blanket of ice.

I just used the formula here:
http://en.wikipedia.org/wiki/Thermal_conduction#Spherical
with k=2.0 for ice, T1=275K for liquid water, T2=168K for Ceres surface average. r2=476km, r1=r2-1000
..for which I ended up with about 6*10^11 watts

and power falling on Ceres based on 150 W/m^2, r=476km, area =pi*r^2
..for which I ended up with 7*10^11 watts.

I would double check those numbers before racing to Ceres to implement this plan.

There is no reason to start that big of course. You could achieve quite a bit with just a ton of hardware so it could be part of an early mission for fuel ISRU or similar. One big unknown is how hard it is to get down to relatively pure ice but we will probably know a bunch more about that in a year.

[the_other_Doug]

I plugged some numbers in and as it happens the solar power falling on Ceres is slightly more than the power required to keep Ceres entirely liquid beneath a layer of 1km of ice...

I will point out that Ceres, being so very low-albedo, does retain a majority of the solar energy that falls onto it.  A non-reflective surface is an absorptive surface, in direct relation to its darkness.

This means that, at least during its sunlight cycle, Ceres absorbs something more than 80% of the sunlight that falls on it.  Which could be warming its interior.

Now, how much of that energy is quickly re-radiated into space as Ceres rotates and the surface alternates from being sunlit to being exposed to dark and mostly-vacuum, I don't have a set of equations to use in order to guesstimate.  But, as dark as it is, Ceres has got to be absorbing a fair amount of solar heat.  It would be interesting to get an idea of its thermal inertia...

[Paul451]

Now, how much of that energy is quickly re-radiated into space as Ceres rotates

If it's at equilibrium then every watt that hits the surface is radiated back out. If it's didn't, the temperature would have increased until it did.¹ You only need the mean surface temperature (168K for Ceres) the temperature a few hundred metres down will be approximately this average². As you go deeper, pressure becomes a factor.

¹ Day side does most of the radiation, being hotter. About 150W/m². The night side drops to around 5W/m². At least according to Mssrs Stefan and Boltzmann.

² This happens on Earth too. Spring water emerges at the average of the annual temperature of the overlying region, barring geothermal input.

[gin455res]

Hmm, what about battery-powered low-isp electrothermal thrusters? Normally these are not practical because they have a maximum mass ratio which is too low for most applications, but in this case, they might be a practical option for a hopper using local water as propellant.

Would a pumped waterjet suffice?

And might it shoot along a couple of long wires passing through guide tubes on the sides of the vehicle.

[Hop_David]

At just 1g acceleration, you reach orbital velocity in about 3km, escape velocity in 5km.

If the track follows a circular arc, the spacecraft would lift off from the track after exceeding orbital velocity.

5 kilometers is about .6º along Ceres surface. To follow a straight line, the end of the track would have to be 27 meters above Ceres' surface. Fairly doable, especially if the track is built atop a gently sloping crater wall.

On an asteroid the inhabitants would have to burrow to protect themselves from radiation. An interesting possibility is tunnels that would form chords from one point on the sphere's surface to another. On entering a tunnel, gravity would pull you to the center of the chord. If the surface were frictionless, inertia would keep you going until you reached the tunnel exit. Thus travel between points A and B could be accomplished with very little energy -- just enough energy to counteract friction.

The most extreme example of such a tunnel would be mohole from the north pole to south pole.



Time of transit along a chord would be the same as the period of a very low circular orbit. In Ceres' case that'd be about two hours and 15 minutes. Transit time for non diametrical tunnel chords would be the same.

If the tunnels have mag rails, the cars could be accelerated during the first part of the trip and slowed before reaching the destination making the trip less than two hours and 15 minutes. Or the rails could accelerate the payload over the entire length, making the tunnel a rail gun shooting payloads from Ceres' surface.

[KelvinZero]

Maybe you can just build a tower tall enough that it throws the spaceship off the end like an atlatl 

http://en.wikipedia.org/wiki/Spear-thrower

[Cedalion]

At just 1g acceleration, you reach orbital velocity in about 3km, escape velocity in 5km.

If the track follows a circular arc, the spacecraft would lift off from the track after exceeding orbital velocity.

5 kilometers is about .6º along Ceres surface. To follow a straight line, the end of the track would have to be 27 meters above Ceres' surface. Fairly doable, especially if the track is built atop a gently sloping crater wall.

On an asteroid the inhabitants would have to burrow to protect themselves from radiation. An interesting possibility is tunnels that would form chords from one point on the sphere's surface to another. On entering a tunnel, gravity would pull you to the center of the chord. If the surface were frictionless, inertia would keep you going until you reached the tunnel exit. Thus travel between points A and B could be accomplished with very little energy -- just enough energy to counteract friction.

The most extreme example of such a tunnel would be mohole from the north pole to south pole.



Time of transit along a chord would be the same as the period of a very low circular orbit. In Ceres' case that'd be about two hours and 15 minutes. Transit time for non diametrical tunnel chords would be the same.

If the tunnels have mag rails, the cars could be accelerated during the first part of the trip and slowed before reaching the destination making the trip less than two hours and 15 minutes. Or the rails could accelerate the payload over the entire length, making the tunnel a rail gun shooting payloads from Ceres' surface.

This was my idea for the moon, until someone mentioned that it is still likely to have a molten core. Given the diameter the deltaV would be impressive. Maybe a shallower tunnel would work.

[JulesVerneATV]

NASA reveals the dwarf planet Ceres had a hidden 'energy source' that may have sparked alien life
https://www.livescience.com/space/astronomy/nasa-reveals-the-dwarf-planet-ceres-had-a-hidden-energy-source-that-may-have-sparked-alien-life

Vast startup will send the Haven-1 space station into orbit in 2025
https://universemagazine.com/en/vast-startup-will-send-the-haven-1-space-station-into-orbit-in-2025/

Ceres is very far away, its possible Artificial Gravity will be needed to keep any animals or humans healthy traveling so many astronomical units