Manned mission to Ceres

[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