Ceres and other more "exotic" Flexible Path destinations

[simon-th]

A request for a separate thread came up on the Phobos discussion thread.

Ceres characteristics:
 - diameter: 950km
 - orbital characteristics: between 2.5 AU and 3.0 AU
 - nearly spherical; escape velocity 0.51km/s
 - equatorial surface gravity: 0.028g (you could probably even walk there - slowly)
 - Ceres probably contains more water than Earth (50% of the volume is probably water)
 - a mean 170K surface temperature and 240K maximum surface temperature
 - possibility of a thin atmosphere - possibly water vapour at poles

So, Ceres is actually a VERY interesting destination to go to - it's even a dwarf planet! Other destinations in the asteroid belt later-stage Flexible Path could visit would be Vesta, Pallas, Hygiea.

The question is, Hohmann transfers take quite some time - so radiation shielding and probably AG would be needed. OR a more direct approach with advanced propulsion systems.

[mmeijeri]

The question is, Hohmann transfers take quite some time - so radiation shielding and probably AG would be needed. OR a more direct approach with advanced propulsion systems.

Or more staging points and faster trajectories with existing propulsion systems. Keeps the advanced propulsion off the critical path (but hopefully on the development track).

[randomly]

We need a high power space reactor. I wonder if that could be an international project coupled with Molten Salt reactor design for earth based power. It's a good time to sell clean energy development projects. However historically space reactor projects are too politically vulnerable and get canceled before completion.

Ceres seems like the perfect opportunity to push ahead with the plan of reducing mission mass by shrinking the Hab size and recruiting dwarf astronauts. A mission to Ceres - the dwarf planet could be used as an irresistible recruiting campaign.

[Lampyridae]

Let's not forget the deltaVee penalty because the thing has virtually no gravity well to skate onto. You have to do it the hard way, firing rockets to match Ceres' solar orbital velocity. Works out to be 9kps to get there, as opposed to about 5kps for Mars orbit (excluding aerobraking). This is a nuclear mission, no question.

[mmeijeri]

This is a nuclear mission, no question.

Not with staging at Phobos. Preposition propellant with SEP and you may well end up with an IMLEO less than that of NTR. ISRU would reduce cost even more. Depots or even just in-flight refueling are a game changer. Even hypergolics could be good enough.

Developing advanced technology is great, but not using the capabilities of existing technologies isn't. Advanced technology should be kept off the critical path as much as possible. And a great deal is possible with existing technology.

[meiza]

Dawn's goal is to characterize the conditions and processes of the solar system's earliest epoch by investigating in detail two of the largest protoplanets remaining intact since their formations. Ceres and Vesta reside in the extensive zone between Mars and Jupiter together with many other smaller bodies, called the asteroid belt. Each has followed a very different evolutionary path constrained by the diversity of processes that operated during the first few million years of solar system evolution.

http://dawn.jpl.nasa.gov

[infocat13]

A request for a separate thread came up on the Phobos discussion thread.

Ceres characteristics:
 - diameter: 950km
 - orbital characteristics: between 2.5 AU and 3.0 AU
 - nearly spherical; escape velocity 0.51km/s
 - equatorial surface gravity: 0.028g (you could probably even walk there - slowly)
 - Ceres probably contains more water than Earth (50% of the volume is probably water)
 - a mean 170K surface temperature and 240K maximum surface temperature
 - possibility of a thin atmosphere - possibly water vapour at poles

So, Ceres is actually a VERY interesting destination to go to - it's even a dwarf planet! Other destinations in the asteroid belt later-stage Flexible Path could visit would be Vesta, Pallas, Hygiea.

The question is, Hohmann transfers take quite some time - so radiation shielding and probably AG would be needed. OR a more direct approach with advanced propulsion systems.

ya you wicked wicked people stealing the Phobos thread for shame. 
its just like trying to talk to EELV ,Direct,stick people at the same time on the same thread.
but anyways some more Ceres papers some new.
http://www.centauri-dreams.org/?p=6529
http://home.comcast.net/~eliws/ceres/files/ReconstructingHSTImagesofAsteroids.jpg
http://wpcontent.answers.com/wikipedia/commons/thumb/5/56/1e6m_comparison_Mars_Mercury_Moon_Pluto_Haumea_-_no_transparency.png/300px-1e6m_comparison_Mars_Mercury_Moon_Pluto_Haumea_-_no_transparency.png
http://www.midnightkite.com/PlanetPovray/planets-3-large.jpg
http://www.astrosociety.org/education/publications/tnl/70/images/layers.jpg

[rklaehn]

Let's not forget the deltaVee penalty because the thing has virtually no gravity well to skate onto. You have to do it the hard way, firing rockets to match Ceres' solar orbital velocity. Works out to be 9kps to get there, as opposed to about 5kps for Mars orbit (excluding aerobraking). This is a nuclear mission, no question.

How did you get the 9kps?

Assuming a propellant depot at EML2 like the one proposed by ULA, I get about 1800m/s for trans ceres injection using an impulsive maneuver at earth flyby, and <4.5km/s for matching ceres orbital velocity using an impulsive maneuver during ceres flyby (it still helps a bit).

So a very conservative estimate for chemical propulsion delta-v including landing would be 7km/s.

For the trip back, you would have to manufacture your propellant on ceres. But that should not be too hard given that there should be plenty of water there. Of course you would need either a nuclear reactor or concentrating solar arrays at that distance to the earth. On the plus side, propellant boiloff would not be a big problem even with LH2.

Edit: I still think that phobos or deimos is the best first beyond LEO goal.

Edit again: I still have to find the error in my back of the envelope calculation, but using this excellent tool (link) from vanilla, it seems that the 9km/s is correct. Too bad.

[Robotbeat]

...
Ceres seems like the perfect opportunity to push ahead with the plan of reducing mission mass by shrinking the Hab size and recruiting dwarf astronauts. A mission to Ceres - the dwarf planet could be used as an irresistible recruiting campaign.

First of all, I think that is genius. In space, there are advantages to being small. Hopefully this doesn't come across as an offensive joke.

[rklaehn]

Turns out that you can reach ceres with 7km/s. It is just that opportunities with such relatively low delta-v are quite rare.

Here is one I found for an arrival in 2026. Arrival C3 at phobos is 29.20 km^2/s^2.

[mmeijeri]

If you involve multiple staging points and SEP for propellant transfer IMLEO is the relevant measure, not delta-v. Crew and propellant would travel with different delta-v's and different Isp's. Due to the high Isp of SEP you can use faster chemically powered trajectories for the crew. This could solve the launch opportunities problem. Multiple staging points reduce the size of the transfer stages that are needed, reduce the needed thrust of the engines and increase the efficiency benefits from SEP.

[rklaehn]

If you involve multiple staging points and SEP for propellant transfer IMLEO is the relevant measure, not delta-v. Crew and propellant would travel with different delta-v's and different Isp's. Due to the high Isp of SEP you can use faster chemically powered trajectories for the crew. This could solve the launch opportunities problem. Multiple staging points reduce the size of the transfer stages that are needed, reduce the needed thrust of the engines and increase the efficiency benefits from SEP.

I would use SEP for a regular fuel shuttle from LEO to EML2, and then use chemical propulsion from EML2 to the rest of the solar system as far as possible. That way you use the SEP where there is lots of sun, and maximize your ROI on your expensive SEP tug.

7km/s is perfectly possible with chemical propulsion. And you can increase the number of launch opportunities and reduce the delta-v even further by using mars gravity assists.

So ceres is definitely within reach of a chemical exploration program staging from EML2.

[kfsorensen]

Edit again: I still have to find the error in my back of the envelope calculation, but using this excellent tool (link) from vanilla, it seems that the 9km/s is correct. Too bad.

Thanks for the shout-out...you beat me to the analysis, but you used my tool!  (so I feel better)

Ceres is a rough place to try to go.  Way out there, 10 degrees inclined to the Sun, no gravity well to help you with a capture burn.

There are near-Earth asteroids that occasionally have very favorable transfers--the irony is that the best ones have orbital elements very close to that of Earth's and because they do they have really long synodic periods (opportunities between visits).  So when they're good, they're really good, but for the next 30 years, forget about it--they become worse than Ceres.

I could see scenarios where we send a crew to a NEO but don't get to visit the same one again for decades.  That's okay--there's plenty more to choose from, and hopefully with that tool you can figure out how to get there and what it will cost you.

[kfsorensen]

Turns out that you can reach ceres with 7km/s. It is just that opportunities with such relatively low delta-v are quite rare.

See how those two "cones" seem to come together in a point, and how that's the time to go?  That's a nodal transfer--it means you launch when you're crossing Ceres's line-of-nodes and you get to Ceres when it is crossing its line-of-nodes.  That shape in the solution space is there because Ceres is inclined 10 degrees to the ecliptic.  That's why conventional Hohmann-transfer calculations aren't very useful for targets that are more than a degree or two inclined to the ecliptic, and you have to really do a three-dimensional trajectory to get anything even close to right.

[mmeijeri]

I would use SEP for a regular fuel shuttle from LEO to EML2, and then use chemical propulsion from EML2 to the rest of the solar system as far as possible. That way you use the SEP where there is lots of sun, and maximize your ROI on your expensive SEP tug.

ROI on the tug and its launch cost are indeed crucial. Using SEP (only for propellant and cargo, not for crew) as far as Mars and maybe even Ceres seems reasonable to me. Total solar power near Mars is about half the value near Earth and I read somewhere that with more modern solar cells the output of the ISS solar arrays could be doubled.

For the initial stages I would not want to depend on SEP from LEO because of the problems of the van Allen belts. I'm sure that will be solved eventually, but I want to keep as yet undeveloped technology as far away from the critical path as possible.

For the same reason I would want to start with hypergolics, which makes having more staging points more useful. SEL-2 and SML-1/2 are obvious choices as advocated by Huntress, Farquhar and others. And conversely, staging makes the staging points themselves more useful. And the staging points conveniently happen to be the consecutive destinations on the Flexible Path.

7km/s is perfectly possible with chemical propulsion. And you can increase the number of launch opportunities and reduce the delta-v even further by using mars gravity assists.

Reusable transfer vehicles stationed at SEL-2 also conserve energy.

So ceres is definitely within reach of a chemical exploration program staging from EML2.

Yep.