Hitching A Ride?

[dragon04]

While it would be slow, has there ever been any thought given to a space probe being sent to a long period comet, landing it and then being re-launched when the comet reaches apogee relative to the Sun?<br /><br />I'm just thinking that you get a free ride to the Kuiper Belt (or sphere if you like) and then power up and accelerate away to the Great Beyond. <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[alpha_centauri]

I'm not an expert but I would have thought that the restraints and dangers, never mind costs of designing such features into a mission would make it more worthwhile building a craft capable of reaching KBO's and further on it's own. <br /><br />Would be an interesting technological feat though.

 

[vt_hokie]

That is an interesting idea, for sure!

 

[najab]

Here's the thing - in order to land on a comet, you have to rendezvous with it. In order to rendezvous with the comet you have to be moving at (very nearly) the same speed as the comet.<br /><br />If you are at the same place as the comet, moving at the same speed and same direction as the comet then you're in the same orbit as the comet - which would take (very nearly) the same energy (read launch vehicle) as launching directly to aphelion.

 

[henryhallam]

Unless you make the spacecraft into a really big and very bouncy rubber ball - then you could get something with similar effect to a slingshot gravity assist! <img src="/images/icons/wink.gif" /> <img src="/images/icons/wink.gif" /> <img src="/images/icons/wink.gif" /> Calculating the acceleration/g-force involved is "left as an exercise to the reader"

 

[mlorrey]

I doubt the rubber ball idea would work very well, but perhaps maneuvering a solar sail into the tail of the comet after perhilion would increase the gas density enough to really billow the sail and get appreciable acceleration enough to rendezvous with the comet.

 

[CalliArcale]

The closest thing I can think of to that is ESA's Rosetta mission and JAXA's Hayabusa mission.<br /><br />Launched last March aboard an Ariane V, Rosetta will go into orbit around Comet 67 P/Churyumov-Gerasimenko in 2014. The primary mission will end in 2015, after the comet passes perihelion. The probe is solar-powered; there's really no chance of it returning any science from the comet's aphelion.<br /><br />Hayabusa has been more in the news lately, having completed (with mixed success) its primary mission in the environs of asteroid Itokawa. Its rover missed the asteroid completely, and although Hayabusa did successfully land on Itokawa and take off again, it is doubtful that it collected a large amount of asteroid material. Still, it's pretty close to the mission profile you've described. Hayabusa will hopefully still be able to return to Earth; JAXA mission controllers are remarkably tenacious.<br /><br />As far as getting a free ride to the outer solar system, hitching a ride isn't the way to do it. It'll take more energy to do that than it would to just go there alone. Either you go with a long-period comet or you go without it; it really makes little difference. There would be value to going along with a comet; you could study how the comet changes with the extreme seasons. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[mlorrey]

The primary benefit to rendezvouing (sp?) with a comet is that it may be a handy fuelling depot. For instance, Comet Tempel, which cruises close to Mars orbit at perhilion and close to Jupiter orbit at aphilion, would be a good object to hitch a ride on for a Jupiter mission. You could refuel from the comets ices, at least enough to assist with fuel needed to insert into Jupiter orbit and get back out again (though you might want to land on a small icy Jupiter moon to refuel again). Jupiter requires more than 57 km/sec dv to insert. I predict that Tempel will eventually become a key logistics point for exploration of the outer solar system.<br /><br />A VASIMR propelled 10 MW nuke plant (combined mass 50 tons) with a 50 ton mission vehicle (total vehicle: 100 tons) could get in on 55,000 lb of fuel. Going in with enough fuel to get out would take another 70,000 lb of fuel, at a minimum for low acceleration high Isp. If this were a manned mission, at top acceleration/minimum dv, this would require 160,000 lb and 290,000 lb respectively. At top acceleration/minimum trip time, this would require more than a million lb of fuel JUST for getting into and out of the Jupiter system. This cannot be done without refuelling at a waystation like Tempel.<br /><br />These sorts of fuel requirements make it obvious that VASIMR is the propulsion of choice. You simply could not make this sort of mission with NTR without tens of millions of lb of fuel, or with chemical fuel (requiring at least twice that of NTR).

 

[CalliArcale]

Now that's a good argument in favor of it! I hadn't thought of that, but it makes sense. It means new technology, but that's okay. <img src="/images/icons/wink.gif" /> We're going to need to make fuel elsewhere if we're serious about expanding off this planet. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[scottb50]

When you rendvous with the comet you will be in the same orbit is in. Why bother landing on it? The gravity would be mostly unfelt. If it was to explore or get samples then I could see it, but to use a comet as a base would take a lot more effort. <br /><br />The propellant required would the same, give or take what it takes to land and takeoff from the comet, as it would be to enter any orbit around the Sun. <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

Scott, go back and read my post. I'm not talking about just landing on the comet. The comet is a means to an end: a location to refuel from the comet's ices, either with water, or hydrogen, methane, etc. in order to reach targets beyond the comets apogee: Jupiter, Saturn, Uranus, Neptune, etc. and to have the fuel to insert significant manned missions into orbit around these planets, as well as the fuel to get back out again and come home. <br /><br />Doing "Space Odessy" style missions with space ships of that kind will not be possible without such refuelling depots. Orbital insertion into orbit around the Jovian planets requires huge delta-v that can only be attempted by VASIMR level technology with stopovers on comets, unless you haul a lot of fuel up from Earth. They are not possible with NTR without huge amounts of fuel, 10-25 times more, than needed by VASIMR.