Chemical propulsion for Europa, Enceladus or Titan sample return?

[RGClark]

This article suggested the SLS could be used for sample return for these outer planet moons:

NASA's Huge New SLS Rocket Could Power Missions Far Beyond Mars
Rob Coppinger, SPACE.com ContributorDate: 30 October 2012 Time: 07:00 AM ET
http://www.space.com/18275-nasa-sls-rocket-potential-missions.html

Here's an article about a planned movie about a manned mission to Europa:

Enticing Trailer for New Movie about a Mission to Europa.
by Nancy Atkinson on November 13, 2012
http://www.universetoday.com/98439/enticing-trailer-for-new-movie-about-a-mission-to-europa/

What would be the delta-V for, for example, a Europa sample return mission? The main thing I'm worried about is the delta-V to escape from the Jupiter system, given here as 59.5 km/s:

Escape velocity.
4.) List of escape velocities.
http://en.wikipedia.org/wiki/Escape_velocity#List_of_escape_velocities

On the other hand we might not need to generate that much by making use of the [ame="http://en.wikipedia.org/wiki/Oberth_effect"]Oberth effect[/ame]. According to this you can get a big boost in your velocity by applying your rocket burn close to the planet. I'm thinking we lift off from Europa, which doesn't require high delta-V because of its small size, and aim our craft towards Jupiter, but to just miss the cloud tops.
Depending on how far Europa is from Jupiter by the time we reach Jupiter we should be near to Jupiter's escape velocity. How much would the velocity be due to gravitational acceleration if leaving from Europa's orbital altitude, headed towards Jupiter?
According to the Oberth effect page if we assume close to 59.5 km/s escape velocity, and leaving from Europa gives us close to that, then by applying say a 10 km/s delta-V we get a 36 km/s delta-v far from Jupiter.


Bob Clark

 

[Urwumpe]

You should better first read how the Oberth effect operates, before making guesstimates how much you gain by it.

Also, the DV is even with it too high for chemical propulsion to work effectively. That number is higher than the total DV used for launching the new horizons probe.

 

[RGClark]

You should better first read how the Oberth effect operates, before making guesstimates how much you gain by it.
Also, the DV is even with it too high for chemical propulsion to work effectively. That number is higher than the total DV used for launching the new horizons probe.

By using the SLS they can't possibly mean to reach 59.5 km/s on return, so the question is how much less does the delta-v applied by the rocket have to be to escape Jupiter's gravity?

Bob Clark

 

[Urwumpe]

By using the SLS they can't possibly mean to reach 59.5 km/s on return, so the question is how much less does the delta-v applied by the rocket have to be to escape Jupiter's gravity?

Bob Clark

First of all, you would have to consider that the "rocket" is in this case a minimal rocket stage with a tiny sample return capsule. The "rocket" would have to stay inactive for years only to arrive at Jupiter.

So, there is not much choice left... chemical propulsion would only work as boost, but a nuclear-electrical propulsion would be needed. Also, you can't get very close to Jupiter, because of its radiation belts, so no strong oberth effect in reality.

 

[Izack]

I'm thinking we lift off from Europa, which doesn't require high delta-V because of its small size, and aim our craft towards Jupiter, but to just miss the cloud tops.

Er, you'll be having [ame="http://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter"]much bigger problems[/ame] than propellant budget if your probe gets that close to Jupiter.

 

[dgatsoulis]

EDIT: I re-wrote this post, because I hate writting math in normal text. I've added pics of the equations and the results.

This looks like an interesting problem, so I wanted to figure out how much ΔV would be needed to make it from Europa to Earth (direct) or from Europa to Jupiter to Earth (Oberth effect).

First let's calculate the ΔV for a Hohmann transfer from Jupiter's orbit to Earth's orbit.

So, a Hohmann transfer from Jupiter's orbit to Earth's orbit costs roughly 5.65 km/s

Now let's calculate the injection burn ΔV from Europa's orbital altitude around Jupiter.

So, the ΔV for the injection burn from Europa's orbital altitude around Jupiter to take us to a transfer orbit to Earth is roughly 6.5 km/s

Now let's find out how much ΔV we need to make that burn from Europa's surface.

So, to get to Earth directly from Europa's surface we need roughly 6.8 km/s

Let's make the second calculation now for the Europa→Jupiter→Earth journey.
We will assume a perijovion of 80*10^6 m , so that we are sufficiently above the atmosphere and we already know that the Jupiter-Earth transfer ΔV is 5.65 km/s

What we need to find is the ΔV for the Europa→perijovion transfer and then the ΔV for the burn at the perijovion.

Already we can see that this type of transfer will cost more ΔV than the direct method, so there is no need to continue this calculation.

A better method would be to launch from Europa heading far away from Jupiter, but not escape. Then make a retrograde burn at the apojovion to lower the periapsis and fall back to Jupiter. This way we would take full advantage of the Oberth effect and it would require a small burn at the perijovion to take us to the transfer to Earth orbit.
We already have the 6.8 km/s ΔV of the direct method, in order to check how much ΔV we will save.

Flytandem has setup a great plan for a Titan→Saturn→Jupiter→Earth journey, which minimizes ΔV using the Oberth effect. You can find it here

 

[RGClark]

EDIT: I re-wrote this post, because I hate writting math in normal text. I've added pics of the equations and the results.
This looks like an interesting problem, so I wanted to figure out how much ΔV would be needed to make it from Europa to Earth (direct) or from Europa to Jupiter to Earth (Oberth effect).
First let's calculate the ΔV for a Hohmann transfer from Jupiter's orbit to Earth's orbit.

So, a Hohmann transfer from Jupiter's orbit to Earth's orbit costs roughly 5.65 km/s
Now let's calculate the injection burn ΔV from Europa's orbital altitude around Jupiter.

So, the ΔV for the injection burn from Europa's orbital altitude around Jupiter to take us to a transfer orbit to Earth is roughly 6.5 km/s
Now let's find out how much ΔV we need to make that burn from Europa's surface.

So, to get to Earth directly from Europa's surface we need roughly 6.8 km/s
Let's make the second calculation now for the Europa→Jupiter→Earth journey.
We will assume a perijovion of 80*10^6 m , so that we are sufficiently above the atmosphere and we already know that the Jupiter-Earth transfer ΔV is 5.65 km/s
What we need to find is the ΔV for the Europa→perijovion transfer and then the ΔV for the burn at the perijovion.

Already we can see that this type of transfer will cost more ΔV than the direct method, so there is no need to continue this calculation.
A better method would be to launch from Europa heading far away from Jupiter, but not escape. Then make a retrograde burn at the apojovion to lower the periapsis and fall back to Jupiter. This way we would take full advantage of the Oberth effect and it would require a small burn at the perijovion to take us to the transfer to Earth orbit.
We already have the 6.8 km/s ΔV of the direct method, in order to check how much ΔV we will save.
Flytandem has setup a great plan for a Titan→Saturn→Jupiter→Earth journey, which minimizes ΔV using the Oberth effect. You can find it here

Thanks for the informative calculations. I knew that the escape velocity from Jupiter's gravity well would be reduced from 59.5 km/s to around 20 km/s at Europa's altitude but neglected to take into account Europa's orbital velocity. I didn't know it was so high, ca. 13 km/s. So the extra delta-v we need for escape is not terribly high. In fact it's just a little more than that needed for the return trip for Mars sample return! See the delta-v's here:

If you add up the delta-V's for the return trip from Mars in that diagram you get 6.4 km/s, assuming full aerobraking at the arrival at Earth.
It is very interesting that with the Falcon Heavy and using Centaur-style upper stages with both high Isp's and high, ca. 10 to 1 mass ratios, that we will have the capability both for Mars sample return and even sample return from the moons of the Jovian planets. Perhaps as early as the first launch of the Falcon Heavy in 2014!
The reason why I wanted to use the Oberth effect is because I wanted to get a short time for the return of the samples. Just getting to Jupiter and Saturn with the Galileo and Cassini missions took 6 and 7 years. I didn't want to have to wait that long for the return of the samples.
How long would the return time be from the Jovian system using the trajectory method without the Oberth effect? How long would it be with the Oberth effect?

Bob Clark

 

[dgatsoulis]

How long would the return time be from the Jovian system using the trajectory method without the Oberth effect? How long would it be with the Oberth effect?

I think you have misunderstood the Oberth effect. The thing that dictates the time (T) of the tranfer is the orbital period (P) of the orbit of that transfer.

T = ½P
P = 2π*sqrt(a³/GM)

T= π*sqrt(a³/GM)

Assuming circular orbits, the time (T) for the Jupiter to Earth Hohmann transfer is 86163200 seconds which is approx. 997.26 days (2.732 years).

where (a) is the semi-major axis of the transfer orbit and M is the mass of the Sun.

All the Oberth effect does, is once you have chosen a transfer trajectory, it helps you minimize the ΔV for the injection burn, provided that you are in a high orbit around the injection planet to start with.

EDIT:
The reason it took so long for Galileo to reach Jupiter is because it used several gravitational slingshots, referred to as the "VEEGA" or Venus Earth Earth Gravity Assist maneuvers.

 

[RGClark]

The Oberth effect also multiplies the applied delta-v of the rocket, resulting in a higher ending velocity than that indicated by the propulsive burn alone.


Bob Clark

 

[dgatsoulis]

The Oberth effect also multiplies the applied delta-v of the rocket, resulting in a higher ending velocity than that indicated by the propulsive burn alone.

I 'm pretty sure that this is not what you mean, but the way I interpreted the statement above is that you apply 1000 m/s of ΔV in a burn and you somehow magically get 2000 m/s out of it. That's not what's going on.

All the Oberth effect does, is once you have chosen a transfer trajectory, it helps you minimize the ΔV for the injection burn, provided that you are in a high orbit around the injection planet to start with.

It is BECAUSE of the Oberth effect that you minimize the ΔV for the injection burn.

In the examples in post #6 I've shown what the relation is between the Transfer ΔV and the Injection ΔV.

Below I've made a spreadsheet for a Europa to Jupiter to Earth journey, taking into account the Oberth effect. The Jupiter to Earth transfer trajectory chosen is a Hohmann transfer that requires 5.65 km/s of Transfer ΔV. I have also calculated the total time of the journey. The burn from Europa is a point impulse burn, not taking into account the moon's rotation.

https://docs.google.com/spreadsheet/ccc?key=0AqL0knq7UaMEdG13eE9URDk2OFJlMmZyMmkwX0NoSXc#gid=0

If you change the values at cells B5 B6 and B7 to the values corresponding to another of Jupiter's moons, you will get a new ΔV and time calculation, corresponding to that moon. You will also need to change the escape velocity from the surface of the moon in column C.

 

[RGClark]

I 'm pretty sure that this is not what you mean, but the way I interpreted the statement above is that you apply 1000 m/s of ΔV in a burn and you somehow magically get 2000 m/s out of it. That's not what's going on.

It's not magic, it's mathematics. The extra energy for the higher velocity is coming from the conversion of potential energy to kinetic energy:

Oberth effect.
http://en.m.wikipedia.org/wiki/Oberth_effect

I like this explanation in Robert Heinlein's book The Rolling Stones as well:

A gravity-well maneuver involves what appears to be a contradiction in the law of conservation of energy. A ship leaving the Moon or a space station for some distant planet can go faster on less fuel by dropping first toward Earth, then performing her principal acceleration while as close to Earth as possible. To be sure, a ship gains kinetic energy (speed) in falling towards Earth, but one would expect that she would lose exactly the same amount of kinetic energy as she coasted away from Earth.
The trick lies in the fact that the reactive mass or 'fuel' is itself mass and as such has potential energy of position when the ship leaves the Moon. The reactive mass used in accelerating near Earth (that is to say, at the bottom of the gravity well) has lost its energy of position by falling down the gravity well. That energy has to go somewhere, and so it does - into the ship, as kinetic energy. The ship ends up going faster for the same force and duration of thrust than she possibly could by departing directly from the Moon or from a space station. The mathematics of this is somewhat baffling - but it works.

http://www.projectrho.com/public_html/rocket/mission.php#id--Oberth_Effect


Bob Clark

 

[dgatsoulis]

Yeah, I already know how the Oberth effect works. I've made a spreadsheet for possible return strategies from Europa, returning to Earth with the lowest possible encounter velocity for a direct transfer, by using it.

 

[RGClark]

Er, you'll be having much bigger problems than propellant budget if your probe gets that close to Jupiter.

I was looking at the NASA channel today when they were discussing the Juno mission. They said they would be able to get quite close to Jupiter by enclosing the sensitive electronics in appropriate shielding:

Juno (spacecraft).

The probe's planned polar orbit is highly elongated and takes it close to the poles — within 4,300 kilometers (2,672 mi) — but then far beyond even Callisto's orbit.[17]
This type of orbit helps the craft avoid any long term contact with Jupiter's radiation belts, which can cause damage to spacecraft electronics and solar panels.[17] The "Juno Radiation Vault", with 1 cm thick titanium walls, will also aid in protecting and shielding Juno's electronics.[18] The spacecraft is planned to complete at least 33 polar orbits, each taking from eleven to fourteen days.
http://en.m.wikipedia.org/wiki/Juno_(spacecraft)#section_5

A fly by using the Oberth effect would also subject the spacecraft to the highest radiation only for a short time.


Bob Clark

 

[RGClark]

This article suggested the SLS could be used for sample return for these outer planet moons:

NASA's Huge New SLS Rocket Could Power Missions Far Beyond Mars
Rob Coppinger, SPACE.com ContributorDate: 30 October 2012 Time: 07:00 AM ET
http://www.space.com/18275-nasa-sls-rocket-potential-missions.html

...

Love planetary science? Dying to explore Europa’s oceans? Meet the man who can make it happen.
Posted on December 20, 2013 | By Eric Berger

This week U.S. Rep. Frank Wolf, a Republican from Virginia, announced he would not run for reelection in 2014. This move makes Houston Republican John Culberson the odds-on favorite to replace Wolf and become chairman of an appropriations subcommittee that oversees NASA.
I have a story in today’s paper that outlines why this is a powerful position, and explains how it is likely to benefit Johnson Space Center. But Culberson’s interest in space go far beyond Houston. He hates the asteroid-retrieval mission. Has strong views about China. And you couldn’t ask for a more ardent proponent of planetary science. Particularly Europa.
http://blog.chron.com/sciguy/2013/1...s-oceans-meet-the-man-who-can-make-it-happen/

This potentially could have Earth-shattering importance as it could prove life on another world.
Also interesting is that such sample return missions from the moons of Jupiter and Saturn could also be mounted by the Falcon Heavy, scheduled for a first test launch in 2014.

Bob Clark

 

[kamaz]

I was looking at the NASA channel today when they were discussing the Juno mission. They said they would be able to get quite close to Jupiter by enclosing the sensitive electronics in appropriate shielding:

It's also worth noting that radiation at Jupiter is bad, but it is not hopeless -- particle energy is below 1MeV:

http://people.virginia.edu/~rej/papers09/Paranicas4003.pdf
http://www.iki.rssi.ru/conf/2009elw/presentations/presentations_pdf/session5/Patterson_ELW.pdf
http://www.google.pl/url?sa=t&rct=j...T1aRTgKv7U4xDEW1rQGafHQ&bvm=bv.58187178,d.bGQ

 

[Furet]

:embarrassed:
I really feel stupid since it looks very basic maths, but I really can’t figure out the way dgatsoulis calculates the injection velocity in this previous post: http://www.orbiter-forum.com/showthread.php?p=391984&postcount=6 (2nd and 3rd capture).

Why is it Vinj = sqrt(Vesc² + DVtr²) rather than Vinj = Vesc + DVtr? I can’t find any explanation in the Internet so far.

:idk:

 

[dgatsoulis]

:embarrassed:
I really feel stupid since it looks very basic maths, but I really can’t figure out the way dgatsoulis calculates the injection velocity in this previous post: http://www.orbiter-forum.com/showthread.php?p=391984&postcount=6 (2nd and 3rd capture).

Why is it Vinj = sqrt(Vesc² + DVtr²) rather than Vinj = Vesc + DVtr? I can’t find any explanation in the Internet so far.

:idk:

Scroll down to near the bottom of this page and read the Hyperbolic Excess Velocity section.

(I highly recommend bookmarking that page and the example problems).

 

[Furet]

Scroll down to near the bottom of this page and read the Hyperbolic Excess Velocity section.

(I highly recommend bookmarking that page and the example problems).

That makes sense now.

Thank you so much. I'll finish this year a little bit less ignorant.