Discussion Uranus and Neptune mission concepts

[K_Jameson]

I'm on verge of finishing the first FOI space probe for the mysterious ice giant Uranus: the Shakespeare/Pope spacecraft.

The probe is an improved version of the Efesto probe, launched at Venus in one of the last "Orbiter Live Missions" broadcasts. A relatively small and cheap orbiter (Shakespeare) with a minimal atmospheric probe (Pope, largely based on the Pioneer Venus Small Probes). Total weight around 2100/2200 kg.

My plan is a direct Hohmann launch with a Jarvis C or Jarvis E, with a Jupiter gravity assist. I'm searching for a realistic launch window. Can you help me?

Mission Requirements:
- direct transfer trajectory with Jupiter gravity assist - REQUIRED
- low DV for the Uranus Orbit Insertion (UOI) - REQUIRED
- launch window in the next ten years - DESIRED
- science at Jupiter: low flyby distance - OPTIONAL

Hopefully, Shakespeare/Pope will be released in the next months, along with the fellow Efesto probe for Venus and the long awaited Galileo II flagship-class mission for Jupiter and Europa.

 

[Malky]

http://clowder.net/hop/railroad/sched.html

There's a download link for Hohmann.xls. when you download and open it, there's place where you should write name of your target, I can't better explain where in document it is but you should be able to find it When you write there 'Uranus', it should give you all needed numbers for Hohmann transfer. But I'm not sure what you mean by Hohmann transfer with gravity assist, as I understand orbital mechanics that's two different things... But anyways, this chart could help

 

[Urwumpe]

According to Wikipedia, the next Launch window to Uranus is in August 2018, but that also depends on mission profile and the C3 of the launch vehicle - with which numbers can we calculate and how much safety factor do you expect?

There should be one launch window for Uranus every year anyway... the question is just what kind of window you need.

 

[K_Jameson]

But I'm not sure what you mean by Hohmann transfer with gravity assist

Earth-Uranus via Jupiter. A hohmann for Jupiter with a slingshot for Uranus. Similar to the New Horizons flight plan, with Uranus instead Pluto at the end. :thumbup:

Oh, and with an orbital insertion around the target planet, instead of a mere flyby.

 

[Urwumpe]

Oh, and with an orbital insertion around the target planet, instead of a mere flyby.

DV available for Orbit insertion?

 

[K_Jameson]

There should be one launch window for Uranus every year anyway...

Indeed, but if Jupiter isn't in the right position, we lose the slinghot: the transfer time increases and the payload decreases dramatically.

DV available for Orbit insertion?

Total DV of the spacecraft is around 1900/2000 m/sec (i have to do a more precise calculation of the weight). I want to save as much fuel as possible after the UOI for a subsequent satellite tour.

 

[Urwumpe]

Indeed, but if Jupiter isn't in the right position, we lose the slinghot: the transfer time increases and the payload decreases dramatically.

But it is a much more relaxed condition as for example a window for a direct transfer. You might loose a perfect slingshot window, but you can still find a less than perfect launch window if the slingshot takes place a bit higher above Jupiter.

That is why I asked for the C3 of the launch vehicle - if we know how much you can maximally provide, we can start investigating different options and optimize for reducing the DV that the probe has to contribute.

Total DV of the spacecraft is around 1900/2000 m/sec (i have to do a more precise calculation of the weight). I want to save as much fuel as possible after the UOI for a subsequent satellite tour.

Understandable. So we should optimize the transfer trajectory for a minimum use of the probe propellant until after UOI.

Can you edit your post above to collect such high-level requirements there? Like "REQ1: Maximize DV left after UOI" or "REQ4: launch window between year 2018 and 2022", numbering the requirements by the importance of your team.

Makes it easier to contribute to a community effort, if you take the role of the "mission owner" there and manage the anarchy a bit.

 

[ISProgram]

I use Trajectory Browser for calculating my hypothetical missions, and while I haven't tested one of these in Orbiter successfully yet (tried last week, as a matter of fact), the planets are more or less aligned in the same positions, so Browser is at least accurate for preliminary planning.

Some Uranus launch windows. I should warn that for your particular scenario you want to minimize delta-V, if you choose to minimize duration you end up with capture delta-V that goes beyond the capability of your spacecraft.

Hope this is of some help.

 

[Urwumpe]

Well the May-02-2021 EJU window there is already pretty good with just 1080 m/s insertion DV (minimum possible seems to be 830 m/s) and 10 years flight time, some more complex tools might find nicer trajectories...

Trajectory Itinerary

Date|ΔV|Description
Earth Departure|May-02-2021|6.76 km/s|C3 = 90.3 km²/s², DLA = -32°
|1.58-yr transfer|
Jupiter Flyby|Nov-29-2022|44 m/s|13.9 km/s relative speed, 32.18 radii altitude
|8.54-yr transfer|
Uranus Arrival|Jun-15-2031|1.08 km/s|

10.12-yr total mission
1.13 km/s post-injection ΔV
7.89 km/s total ΔV

Solar range: 1.01 - 19.12 AU
Earth range: 0 - 20.14 AU





...just looking, I had a nice planning tool on my old PC...

 

[K_Jameson]

Well the May-02-2021 EJU window there is already pretty good

I agree!

 

[Urwumpe]

I think the tool was NASA GMAT, will try it out if it was the same that I had used for planning some Orbiter missions.

EDIT: Too bad I currently have to write some stuff for university right now... also writing a small tutorial on how to use GMAT for Orbiter mission planning could be cool, it looks like this was the software I used, but it improved a lot since I last saw it.

 

[Nicholander]

Also, a Chapman Modules scenario someone posted on the Chapman Modules thread (It isn't included in the mod, but it is in the thread for it), has a Uranus orbiter with a Jupiter flyby, and in this case it launches on June 12, 2034. But, it may require too much delta-v perhaps, I don't know. The choice is yours.

 

[K_Jameson]

Can you edit your post above to collect such high-level requirements there? Like "REQ1: Maximize DV left after UOI" or "REQ4: launch window between year 2018 and 2022", numbering the requirements by the importance of your team.

OK! I did! :thumbup:

 

[Urwumpe]

For the planning:

Do you already have some information about propellant tanks and thrusters? Also I need more information about the mass properties for GMAT to optimize things.

Next, which ground stations would be interesting for you (I am playing around a bit in GMAT there, lets see what I can calculate on my notebook with it)

 

[K_Jameson]

Fuel is circa 950 kg of N2=4/MMH. Isp 330 sec. Total mass of the spacecraft is around 2500 kg included the 300 kg payload adapter and the 90 kg atmospheric probe.

For the launch vehicle: it is a Jarvis C but i have some problems to calculate the C3; anyway, with the payload stated above, we have around 7 km/sec of delta V available after achieving the LEO parking orbit. Sufficient with large margin for the Jupiter transfer.

 

[Urwumpe]

Fuel is circa 950 kg of N2=4/MMH. Isp 330 sec. Total mass of the spacecraft is around 2500 kg included the 300 kg payload adapter and the 90 kg atmospheric probe.

For the launch vehicle: it is a Jarvis C but i have some problems to calculate the C3; anyway, with the payload stated above, we have around 7 km/sec of delta V available after achieving the LEO parking orbit. Sufficient with large margin for the Jupiter transfer.

Will the atm probe be separated after or before UOI?

 

[rseferino]

I have chosen a profile aero-braking, as Neptune Orbiter: http://www.orbiter-forum.com/showthread.php?t=34860

But ... is mandatory Jovian direct transfer? EVJU a flight would take a year or two more but could allow increased payload.

 

[ISProgram]

I use this calculator for delta-v calculation, it seems to be very accurate.

Urwumpe has a point, that 90 kg of atmospheric probe might need to be gone before UOI, it should be gone by then, since Galileo did the same thing with its probe and somewhat doubt that your probe has a solid retrorocket.

Anyhow, with that probe attached, you only have 1,829.47 meters of delta-V on you, excluding the payload adapter. Without that 90 kg, you have 1,936.11 meters of delta-V, which is much better.

Not sure about the delta-V requirements for UOI, but if you use any of the ones from Trajectory Browser, then the 6/7/34 window is highly desirable, since it has the lowest delta-V requirement for UOI, and generally fulfills all of your required prereqs, with only the Jupiter flyby distance (25.86 radii) and the launch window (2034, twenty years from now) being the only real issues.

Urwumpes already noted the best trajectory you should follow if you want to save as much propellant after UOI for that moon tour. Maybe use targeted flybys of the large moons (Titania, Oberon, etc.) to save delta-V the same way Cassini's been using Titan for the last 10 years?

As far as Browser is concerned, you won't be able to get a good launch window out to 2024, the delta-V requirement is too much.

 

[boogabooga]

I was the one who tried almost this exact problem with the Chapman probe last summer: http://www.orbiter-forum.com/showthread.php?p=475182&postcount=14
I conducted the mission with plenty of Delta-V for flybys.



After about two days with TOT, I would concur that the June 2034 launch window is best in the 2030s. However, I did not search for a solution in the 2020s. It gives you an approximately Hohman transfer to Jupiter, followed by an approximately Hohman Jupiter-Uranus transfer. The Jupiter-Uranus transit time is LONG.

Have a close approach at Jupiter and a low capture Delta-V at Uranus are mutually exclusive. The closer you get to Jupiter, the faster you will be flung out to Uranus, and the higher the capture velocity will be. IRC, the double Hohman transfer has a Jupiter pass radius at about the distance of Callisto. Any closer, you will need more delta-V somewhere.

An additional consideration is the plane alignment of the moons upon your arrival. Remember, Uranus is tilted on its "side". There will be one point in its orbit where you can arrive at Uranus in the plane of the moons' orbits. While this doesn't occur from the 2034 launch, you get the second best situation IMHO, a polar orbit. I described in the mission description how to set up for perpendicular encounters and I was able to get several.

BTW, Uranus' moons are puny, don't expect constructive trajectory changes from them.

Edit:

The purpose of the polar orbit at Uranus is so that you can have all of your moon encounters at either your periapsis or your apoapsis. This lets you to set up encounters with other moons using all near Hohman transfers, and is an efficient way to explore the Uranus system.

 

[Urwumpe]

Have a close approach at Jupiter and a low capture Delta-V at Uranus are mutually exclusive. The closer you get to Jupiter, the faster you will be flung out to Uranus, and the higher the capture velocity will be. IRC, the double Hohman transfer has a Jupiter pass radius at about the distance of Callisto. Any closer, you will need more delta-V somewhere.

Correct - I get something around 32 Jupiter radii as distance for the swing-by to Uranus with a low insertion DV.

An additional consideration is the plane alignment of the moons upon your arrival. Remember, Uranus is tilted on its "side". There will be one point in its orbit where you can arrive at Uranus in the plane of the moons' orbits. While this doesn't occur from the 2034 launch, you get the second best situation IMHO, a polar orbit. I described in the mission description how to set up for perpendicular encounters and I was able to get several.

Much better would be just doing the UOI at perigee into a high elliptic orbit and then change the plane at apogee. Important would be then just the RAAN - how should be the visibility of the probe from Earth, are radio black-outs permitted, etc.