New Mars Forums

It takes much less delta vee to capture incoming cargo to a long elliptical orbit than it takes to capture to a circular orbit. If the apogee is high enough, the perigee velocity is darn near escape velocity.

For capture the apogee needs to be within Earth's sphere of influence (SOI) which is about 922000 km altitude. But the apogee also needs to be low enough to avoid having the orbit destroyed by lunar perturbations. I've seen 1/2 lunar distance (LD) suggested for maximum apogee.

I don't like this limitation. Perhaps there are stable moon resonant orbits with higher apogees. The Hilda asteroids are in stable orbits resonant with Jupiter and Pluto is in a stable orbit resonant with Neptune. (Although some resonant orbits are decidedly unstable as evidenced by the Kirkwood gaps in the asteroid belt and also the gaps in Saturn's rings)

Here is a moon resonant orbit I like a lot but don't know if it's stable or unstable:
Period: 1/3 moon's period (about 9 days)
perigee: 300 km altitude
apogee: 356544 km altitude

The apogee would come close to the L3, L4 and L5 points, cycling through all three over a lunar period. So it could be a ferry between LEO and high orbital colonies. Fuel would be saved if radiation shielding, air, water, etc. don't need to be boosted each trip through the Van Allen belt.

But here's the best part: Capturing cargo and passengers incoming from Mars to this orbit at perigee would take only .49 km/sec delta vee. Ditto for sending stuff to Mars.

If near earth asteroids are mined for volatiles, metals, etc., these would be a good place to send these resources since they could be captured at perigee with relatively little delta vee.

If they served the L3, L4 and L5 points as I mentioned earlier, there could be three of them, spaced 120 degrees apart. So there are more launch windows.

But I don't known how stable this orbit it. If it's one of the decidedly unstable resonant orbits, then station keeping might well be too expensive. But I'm hoping it's a stable resonant orbit.

I'd like to take a shot at it (am not guaranteeing delivery though). Offer away.

Most of the Centaur orbits are prograde. Crashing two prograde orbits wouldn't shed much angular momentum. If you were able to shed 3 km/sec or so via collision, I don't think you'd have an ocean of cleaning fluid but a cloud. With much of the gas molecules/plasma atoms having velocity greater than the small cometary body's escape velocity.

If you can get a body from this region to Mars, it'll be moving about 10 km/sec on arrival.

Trip times would be 30 years or so.

High velocity impacts could well blast loose more Martian atmosphere than the impactor contributes.

Why do people keep suggesting KBOs, Centaurs or comets? There are likely icey bodies at Jupiter's L4 and L5 points as well as the outer Main Belt. Since these are closer to Mars in Sol's gravity well, the delta vees are smaller.

Rob,

The Delta-Vs come from my Hohmann Excel spreadsheet
http://www.clowder.net/hop/railroad/Hoh … ohmann.xls
The periapsis and apoapsis cells are treated as distance above planet's surface. So if you get Phobos or Deimos distance from Mars center (for example) be sure to subtract Mars' radius to get altitude.

This version doesn't include elliptical apoapsis velocity or circular orbit velocity at apoapsis. I hope to upload an updated, improved sheet soon.

The spreadsheet assumes coplanar, circular orbits which isn't too bad an approximation except for Pluto, which is why Pluto's excluded.

Let's see, if periapsis is 300 km above Mars surface and apoapsis 5981 km, I get 1.42 km/sec to shed enough velocity for Phobos transfer and about .52 km/sec to circularize orbit at Phobos (pretty close to your figures). A total of 1.94 km/sec.

However if I set periapsis at 5981 km, a single burn to circularize takes about 1.88 km/sec.

I think the only advantage of entering an elliptical rather than a circular orbit in this case is delta vee savings from aerobraking.

If I remember right, Kim Stanley Robinson terraforms his Mars with KBOs. To send bodies at 40 AU to Mars you'd need 3.4 km/sec. Velocity on reaching Low Mars Orbit is 10.5 km/sec . It would take about 47 years for a KBO to fall to Mars from a 40 A.U. orbit. Getting to KBOs would be very hard. We still haven't sent a Discovery mission to Pluto so far as I know.

I would use the asteroids at Jupiter-Sun L4 and L5 points (aka Trojans)

These are far enough from the sun to be ice rich.

Delta vee to send them on a Hohmann journey to Mars is 4.27 km/sec. Likely the asteroid's own resources can provide fuel and reaction mass.

When a Trojan arrives in Low Mars Orbit, it is traveling 7.6 km/sec. If Mars' atmosphere sheds 2.8 km/sec or more, the body is captured into  elliptical orbit. Then each periapsis the body would again graze the atmosphere, gradually losing angular momentum Until finally the Trojan penetrates the Martian atmosphere one last time at about 3.5 km/sec.

For one body of Trojans, Hohmann windows occur each 2.24 years. But Mars could receive Trojans twice as often since there are two populations (the leading and trailing or L4 and L5). It takes a Trojan about 3.1 years to fall to Mars from it's original 5.2 AU orbit.

A simple circumfrential power grid would be a huge structure especially about the equator and lower latitudes. And, unless your lines are superconductors, you wouldn't be able to send power much past the terminator. Line loss is a pain in the butt for power providers.

The composition of most NEOs remains unknown. It is thought most are recent arrivals from the Main belt or the Kuiper Belt thrown down into the inner system by perturbations from Jupiter or Neptune. One asteroid, 1979 VA is an extinct comet. 1979 VA is actually a rediscovery of the Wilson-Harrington comet. As comets outgas, it's believed their surface becomes a thicker and thicker mantle of insulating dust. So the extinct comets are thought to have volatile ices beneath their insulating mantles.

An example of a carbonaceous NEO is 1998 KY26
http://antwrp.gsfc.nasa.gov/apod/ap0209 … 20919.html

Since their composition remains largely unknown, I advocate a series of Discovery missions to the most easily accessible NEOs. If the probes are mass produced and miniaturized (like SMART-1), the unit cost per asteroid prospector probe might be quite low. Gathering an inventory of available NEO resources would be well worth the investment, in my opinion.

Some NEOs tumble chaoticly (Toutatis for example) Putting Photovoltaics (or even landing) on such may be a problem. But many may spin about a single axis (like the earth or moon). In such cases it'd be possible to put a rotating photovoltaic array on ball bearings on the north and south poles of the asteroid. You could also put arrays in close orbit about the asteroid and send power to rectennas on the asteroid's surface.

Yeah! I'd like to see one on Mount Chimborazo, Ecuador. By the time you fire your rocket engines, you'd already be going mach .9 and be above much of the troposphere.

And at the equator you're already going .5 km/sec

It is tempting to bring asteroids close to Earth. The deeper into the gravity well you go, the more the Oberth effect can be exploited and the more delta vee is saved. Also aerobraking is a good source of delta vee.

My suggestion has been to set a ceiling on the size of imports to cislunar space. Some believe Tunguska was about 100 meters in diameter. Maybe a 50 meter diameter would be a good ceiling.

I have been fired up about the 1.5 year cyclers for some time (aka the Niehoff VISIT 2 cycler). You are reaching the same conclusions I have that it could visit both Earth and Mars repeatedly. As you note, the delta vee isn't much more than Hohmann transfer orbit.

If the cycler is an asteroid nudged into the cycler orbit, folks on this slow flight could indeed be put to work for science and industry. It's believed asteroids and comets are much less changed since the solar system's formation than planet surfaces. They are of great scientific interest. Also many have very pure metals and some have water and carbon compounds.

There is a problem though: Not only does the asteroid have to be at the right place, it must at the right place at the right time.

There are cycler orbits that regularly fly both Earth and Mars. Buzz Aldrin has designed one that passes by both Earth and Mars each synodic period (about 2 & 1/7 years). The "castle" would be be well stocked with radiation shielding, food, air (maybe even self sustaining closed ecology life support systems). Then when the castle is in the neighborhood of either Earth or Mars a much less massive "taxi" can be sent to the planet (or from the planet to the castle). However Aldrin cyclers demand a lot of delta vee from their taxis since it passes Mars with a relative velocity of about 12 km a second.

Then there are two types of cyclers that pass by the planets somewhat less frequently but still regularly. Niehoff VISIT 3  passes by the earth every 3 years and Mars every 7.5 years. Niehoff VISIT 1 earth every 5 years and Mars 3.75 years.

I talk about nudging asteroids into Niehoff cycler orbits on this page:
http://www.clowder.net/hop/railroad/sch … sched.html