Uranus Orbiter, The other proposed ice-giant mission Options

[Rob Pinnegar]

Since the Neptune Orbiter thread has started to veer into talking about a Uranus orbiter as well, it seemed like a good idea to start a topic for Uranus.

[tasp]

Without incurring copyright snags, of course, could I field a question about the ideas in the paper?

The portion available through the link ends with an intriguiging acknowledgement that the vehicle could enter orbit about Ariel after ~40 loops around Uranus.

Is this characteristic of the orbit tour similar (at least broadly) to the clever trajectory Messenger is utilizing to eventually end up in orbit about Mercury?

I realize the mass ratios of Sun - Mercury - Venus - Earth are quite different, but is there a correlation between the flight plans?

Amazing article, regardless!

[Guest_AlexBlackwell_*]

Without incurring copyright snags, of course, could I field a question about the ideas in the paper?

The portion available through the link ends with an intriguiging acknowledgement that the vehicle could enter orbit about Ariel after ~40 loops around Uranus.

Is this characteristic of the orbit tour similar (at least broadly) to  the clever  trajectory Messenger is utilizing to eventually end up in orbit about Mercury?

I realize the mass ratios of Sun - Mercury - Venus - Earth are quite different, but is there a correlation between the flight plans?

Amazing article, regardless!

Darn, wouldn't you know that I don't have a copy of the paper available on my system at the moment

That said, I'll review it when I get home but from what I recall, the main concept behind the end-of-tour plan to insert into orbit at Ariel is based on orbital pumping and cranking, which not only changes inclination from the initial Uranian insertion, but reduces relative velocity so that the deterministic delta-V for insertion at Ariel can be handled by the orbiter's propulsion system. I can't remember whether the scheme also utilizes any "third-body" effects from Uranus or "fuzzy boundaries" but these might possible as was planned for the original Europa Orbiter insertion in europan orbit.

Whether this resembles, even in a broad sense, the MESSENGER trajectory through the inner solar system, is, I guess, in the eye of the beholder.

[tasp]

Darn, wouldn't you know that I don't have a copy of the paper available on my system at the moment 

That said, I'll review it when I get home but from what I recall, the main concept behind the end-of-tour plan to insert into orbit at Ariel is based on orbital pumping and cranking, which not only changes inclination from the initial Uranian insertion, but reduces relative velocity so that the deterministic delta-V for insertion at Ariel can be handled by the orbiter's propulsion system.  I can't remember whether the scheme also utilizes any "third-body" effects from Uranus or "fuzzy boundaries" but these might possible as was planned for the original Europa Orbiter insertion in europan orbit.

Whether this resembles, even in a broad sense, the MESSENGER trajectory through the inner solar system, is, I guess, in the eye of the beholder.

Have reviewed the Heaton/Longuski paper (Thanx!) now and have some comments.

The 'clever bit' of the Messenger trajectory, gravitational interaction with the target object to facilitate orbital insertion, isn't employed at Ariel. This technique is not addressed in the paper, but since utilizing it would take quite a while (if it were even possible at Ariel) and the paper was assuming 2 year long orbital missions the omission is not surprising. Also, the 1km/sec 'burn off' at Ariel doesn't seem excessive anyhow, so the utility of the technique at Ariel is less appparent. That the technique works at Mercury may be due more to Mercury's high density alowing the craft to approach closer to the planets center of mass to 'realize the math' than may be possible with an icy body like Ariel. It is not clear (to me) how the mass ratios and distances scale for this technique from sun/Mercury to Uranus/Ariel.

I am also amazed with the Heaton/Longuski trajectory in that in 2 years, 40 (!) encounters with Oberon, Titania, Umbriel, and Ariel are possible. A significant truth revealed in the paper is that since the Uranian system is 'scaled' smaller than the Galilean satelllites, useful distant flybys of Uranian moons also occur more frequently than they did for the Galileo spacecraft.

Inferring to Cassini, it seems the mass ratio of Saturn/Titan being so different from that of Jupiter or Uranus does allow Cassini much more flexibility in changing it's inclination around Saturn. I had wondered why this was not done with Galileo at Jupiter, and it seems many more satellite flybys would be required for a given inclination change than for Cassini at Saturn.

It does seem that an interesting mission could be orbited at Neptune following the Cassini style tour.

Also, granted the enormous delta vee needed to effect orbit insertion around Pluto, once that is achieved, an interesting mission at Pluto is possible utilizing Charons gravity for orbit shaping. Close observations of Pluto and Charon at a variety of inclinations seems quite feasible, and arbitrarily close approaches to the 2 new satellites seems 'easy' now. The big problem remains though, the difficulty in achieving orbit around Pluto due to the high approach speed of any reasonable spacecraft.