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selvaarchi
2014-Dec-23, 02:23 AM
Currently, the favored method for getting a spacecraft into orbit around a planet is the "Hohmann transfer" but a new method called "ballistic capture" could save space agencies time and money. It could and has been applied for moons or other space objects.

http://www.marsdaily.com/reports/New_idea_for_transporting_spacecraft_could_ease_tr ip_to_Mars_999.html


Currently, the favored method for getting a spacecraft into orbit around Mars is the "Hohmann transfer." After rocketing through the Earth's atmosphere, the craft make a beeline for the Red Planet, barreling through space at high speeds. As it approaches Mars, its thrusters fire in the opposite direction -- slamming on the brakes and swinging the craft into orbit.

The Hohmann transfer is a highly effective move -- road-tested and reliable. But it is expensive and time specific. Launches are limited to a brief window when the orbit and rotation of Earth and Mars are just right.

Ballistic capture, on the other hand, would allow a more flexible launch window. It would also do away with the fuel-guzzling that Hohmann's high-speed braking requires. Instead of rocketing straight at Mars, a ballistic capture technique would see the spacecraft launched out ahead of Mars' orbital path. It would gradually slow and hold in place, waiting for Mars to swing by -- the Martian gravity pulling the craft into orbit as it approached.

Noclevername
2014-Dec-23, 03:32 AM
Not new. Also, the article's description of a Hohmann orbit sounds a little wonky.

selvaarchi
2014-Dec-23, 09:05 AM
Not new. Also, the article's description of a Hohmann orbit sounds a little wonky.

It says so in the article. From the article, I gather that it is being given a more solid mathematical/scientific foundation.


NASA has used the ballistic capture technique on one of its lunar missions -- the GRAIL mission in 2011. The European Space Agency also used the technique for its SMART-1 lunar mission in 2004.

IsaacKuo
2014-Dec-23, 01:40 PM
The technique is interesting for a number of potential applications, but it requires more delta-v than Hohmann transfers, at Mars (as shown in the paper). I think it's more interesting for applications where you lack the high acceleration required for Hohmann transfers. In particular, diverting an asteroid into Earth orbit is a potential application.

It also requires more time than a Hohmann transfer, but that's not so important for unmanned applications.

Extracelestial
2014-Dec-23, 06:02 PM
Currently, the favored method for getting a spacecraft into orbit around a planet is the "Hohmann transfer" but a new method called "ballistic capture" could save space agencies time and money. It could and has been applied for moons or other space objects.

http://www.marsdaily.com/reports/New_idea_for_transporting_spacecraft_could_ease_tr ip_to_Mars_999.html

Hello Selvaarchi,

the quoted article doesn't appear to be correct. It has several "small" errors:

1 It would also do away with the fuel-guzzling that Hohmann's high-speed braking requires: this is wrong.
The reason a Hohmann trajectory is used is that it is the path that requires the least amount of energy; i.e. fuel.
2 Instead of rocketing straight at Mars, a ballistic capture technique would see the spacecraft launched out ahead of Mars' orbital path. It would gradually slow and hold in place, waiting for Mars to swing by
The same applies for the Hohmann transfer (which btw. isn't straight) where a planet pulls at the craft. However, it wouldn't be held in place as no object on a trajectory is stagnant.
3 ballistic capture isn't perfect. It takes much longer than the typical six-month straight shot that has spit a number of Mars current orbiters into their paths around the Red Planet.
No trajectory is ever straight as long as there is gravity.
4 There seem to be however more launch windows with ballistic capture and this is the most interesting issue.

I've got the impression that a very enthusiastic journalist wrote this article about the merits of a new type of transfer orbits.

Cheers
Ex

cjameshuff
2014-Dec-28, 05:36 PM
As others said, the description of the orbital mechanics involved is very inaccurate. A vehicle performing a Hohmann transfer does not make a beeline for its target, it enters an elliptical orbit that reaches the target after half an orbit. A more efficient approach is a bielliptic transfer, which involves an additional burn and going through parts of two different elliptical orbits before rendezvous with the target.

Ballistic capture trajectories exploit perturbations from multiple bodies on objects following particularly unstable trajectories. They can get a vehicle to a location with lower overall delta-v...eventually, by a sometimes very indirect route. The Hiten probe was put into lunar orbit by this technique, in a maneuver that took 5 months to complete instead of the 3 days a Hohmann transfer would have needed. They are not new...this was done in 1991. They are not at all immune to launch windows, though there may be less of a cost to missing the ideal launch time. They do not involve gradually slowing to a stop (just talking about such a thing is a sign of poor understanding on the writer's part), and doing so would not reduce the delta-v required. They can allow lower levels of thrust to be used, which can make them a good fit to engines with high propellant efficiency but low thrust.