Retrograde High-Solar Orbit Rescue

[Mars-Bound Hokie]

I just took a contract to rescue a girl from a retrograde solar orbit. More details in the chart below.

 

AND FOR GOD'S SAKE, READ THE CHART BEFORE YOU ASK "WHAT ARE THE TARGET'S ORBITAL PARAMETERS?"

MISSION BRIEFING
CURRENT TIME: Y54D295 – 1H20M
Name	Haycal Kerman
Specialty	Pilot
Craft Model	Mk. I Crew Cabin
Land-by Date	Y74D292 – 0H46M
Solar Apoapsis (m)	53,476,467,987
Solar Periapsis (m)	41,561,681,152
Inclination (degrees)	~ 177

 

If I complete this rescue mission successfully, I'll earn 178,200 total (this is the rewards minus the reputation taxes)

 

I'm a bit clueless on how I should proceed with this mission. Worst of all, I have no idea how to build the rescue craft. I had the idea to use ion propulsion for the final rescue craft, but I also need the energy and power generation (especially RTGs) to go with it. Aside from that, I have no idea how to proceed - or if ion propulsion would even be enough.

 

Does anyone have any ideas on how I should:

1. Construct my spacecraft.
   1. Propulsion source
   2. ISRU or not?
2. Action plan:
   1. When to launch
      1. Launch when Kerbin is at a certain spot relative to Haycal?
      2. Blast off at morning or night at the KSC
   2. What to do after leaving Kerbin's SOI
      1. Gravity assist/s (I'm bad at those)?
      2. Refueling?

 

Any and all help is greatly appreciated. Thank you.

Edited January 16, 2020 by Mars-Bound Hokie
I got sick of people asking about orbital parameters while they're right in front of them.

[Laie]

5 hours ago, Mars-Bound Hokie said:

I'm a bit clueless on how I should proceed with this mission.

Standard approach: go out to a high AP for changing directions. 6y to get there, 6y to get back, should be somewhere outside of Eeloo already. Though that's probably not far enough to make the maneuver truly cheap.

Alternative 1: get some help from Jool. Won't suffice for a complete reversal, but certainly helps. Might be just as cheap or expensive as the standard approach.

Alternative 2: just brute-force it. In first approximation, it should be on the order of 20km/s. I just plotted a plan that will leave Kerbin for a sub-Moho PE with the Sun, already retrograde, for 15km/s -- from there, it's another 4km/s to your target orbit.

Attention: IIRC it is not possible to aerobrake on Kerbin from a retrograde orbit. Check the "Rescue Burberry" challenge for details, @ManEatingApe has just posted the link as I write this. AFAIK you should be no faster than 8500m/s when hitting the atmosphere.

5 hours ago, Mars-Bound Hokie said:

I had the idea to use ion propulsion for the final rescue craft, but I also need the energy and power generation (especially RTGs) to go with it.

Use fuel cells. If I got the maths right, consuming one large Xenon tank worth of propellant will require 13.2u of liquid fuel + the appropriate amount of oxidizer -- that's less than one Oscar-B tank. Seems I didn't get it right, experimentally it's more like one FLT-200 tank for 5700u of Xenon.

I've just thrown together a quick mock-up (poodle, then nuke, then ion) and ended up with a vessel of 20t dry + 80t propellant for the required delta-V. That's easy if you have a fuel source in space, otherwise I'm afraid that you won't make much, if any, profit from this contract.

Edited January 15, 2020 by Laie

[AHHans]

Is this a stock game, or do you use any relevant mods?

Do I see that correctly that poor Haycal is in an orbit at about the same distance to the sun as Dres?

I haven't some such a rescue, but I did two rescues from low solar orbit. My first try kind-of failed and I needed a number of additional pusher craft to get them back. (Whenever I though "this is surely enough dV" I was wrong.) My second try used a craft that had 27 km/s dV after refueling in LKO. Of that there were about 7 km/s in a nuclear stage and 20 km/s in a stage with ion engines. (Not too much TWR in the ion engines, but fuel for 3.3 hours at full (*cough*) acceleration...) You can probably take your time for the burns (i.e. effective TWR isn't really important) so that you can do with limited EC generation for the ion engines. (Have a good amount of batteries, burn in physics warp until they are empty, recharge them in time-warp, rinse and repeat.)

How much time can you take to get the rescue done? Without gravity assists I guess the least amount of dV would be needed if you went to really far out from the sun (where the orbital velocity is low), and do your plane change (aka orbit reversal) there into an orbit with its PE on Haycal's orbit. But that can take a few in-game decades.

You also need to think about if you can risk aerobraking with 10 km/s or more at Kerbin on the way back. I've never tested the limits of what can be done there. But if you don't need to reverse your orbit again after picking up Haycal then you can save nearly half the dV (and time).

(O.K. that's it for now. I may add more at a later time.)

 

[Signo]

You may find hints in this old old old piece of Kerbal history.

If I recall correctly, a Jool slingshot was key to achieve the trick with a reasonable craft.

 

 

[Mars-Bound Hokie]

10 minutes ago, AHHans said:

Is this a stock game, or do you use any relevant mods?

It's a stock game, all right. If I was looking for "relevant mods," I'd probably get one with a hyperdrive. That would kick ass.

 

11 minutes ago, AHHans said:

Do I see that correctly that poor Haycal is in an orbit at about the same distance to the sun as Dres?

More or less: full details are on the chart posted in the original post.

 

• Excuse the mess, but this shows where Haycal's wreckage is relative to the sun.

 

14 minutes ago, AHHans said:

How much time can you take to get the rescue done?

As you can see in the chart, I have 20 in-game years to complete the rescue.

[AHHans]

23 minutes ago, Mars-Bound Hokie said:

It's a stock game, all right. If I was looking for "relevant mods," I'd probably get one with a hyperdrive. That would kick ass.

Well, if you were already using any mods that change the solar system or do other changes to the game balance then that would have affected the best way to do this.

23 minutes ago, Mars-Bound Hokie said:

As you can see in the chart, I have 20 in-game years to complete the rescue.

Ah, O.K. The way that it is listed in the chart is a bit unfamiliar to me. 20 in-game years is not all that much to go hanging around in the outer solar system...

To answer some more of your questions in the original post: I don't think a particular launch time will make a big difference for the approach I outlined earlier. You can easily change how long you hang around in the outer system by going a bit farther out or not. And I don't think there is much that you can do with an ISRU on the rescue craft. All the planets are going the same way around the sun, and Haycal is going the other way. (What might work is using a large asteroid with a high ore-fraction as an efficient fuel-tank. But that is a bit far fetched...)

 

Edited January 14, 2020 by AHHans

[ManEatingApe]

This challenge has plenty of entries that may inspire you:

 

Edited January 15, 2020 by ManEatingApe

[Mars-Bound Hokie]

2 hours ago, Laie said:

Alternative 2: just brute-force it. In first approximation, it should be on the order of 20km/s. I just plotted a plan that will leave Kerbin for a sub-Moho PE with the Sun, already retrograde, for 15km/s -- from there, it's another 4km/s to your target orbit.

That was my idea. I am bad at plotting gravity assists, nor do I particularly care for them. Besides, I'm on a time budget here.

 

2 hours ago, Laie said:

Attention: IIRC it is not possible to aerobrake on Kerbin from a retrograde orbit.

Can an inflatable heat shield protect a small capsule when doing a direct splashdown trajectory?

 

 

Here's my idea 1 for the rescue mission? Do you think it will save the girl with a brute force approach? I also made sure to point out the inflatable heat shield protecting the capsule.

[Laie]

7 minutes ago, Mars-Bound Hokie said:

Here's my idea 1 for the rescue mission?

I'd say this should be fully enough. 2 comments:

• reconsider your solar panel configuration: as it is, at most 2 can really catch the sun at any given time. Out at Dres the sunlight is already dim enough (quick check, less than 3EC/sec from one Gigantor) -- you want to arrange them so that you can expose them all.
• Have you tested if capsule + heatshield will be aerodynamically stable? The biggest heatshield is for naught if it acts as drogue.

Talking about heatshields: As I remember, there is a speed limit for heat shields: above 8500m/s they will blow up instantly, no matter what, from exceeding the skin temparature limit. Checking the stats: I don't think the deflatable one will fare much better.

It pays to bring a larger than necessary size, just for the extra drag and stopping power. A Mk1 Pod & Shield simply doesn't have enough drag for capture. However, a 2.5m shield will do nicely. You also don't that much ablator: certainly less than half, possibly as little as 240u. Good way to literally shave off about 500kg...

[AHHans]

5 hours ago, Mars-Bound Hokie said:

Can an inflatable heat shield protect a small capsule when doing a direct splashdown trajectory?

Have you activated G-force limits in the difficulty options?

[RizzoTheRat]

I've never thought about it on rescue contracts, but is the time limit the time to make the rescue, or the time to return them to Kerbin?  The former would be nice but I'm guessing it's the latter.

If my maths is right (big disclaimer :D) Haycals orbit has a period of 6.5 years, meaning you don't really get a lot of choice where you intercept, and her speed's varying from 4400m/s at Ap to 5600 at Pe...in the opposite direction

You can also calculate the maximum theoretical dV for a given stage, which is around 17000m/s for the NERV and 7500 for LFO engines.  So my gut feeling is you should be able to do this with the NERV but not with any LF/Ox engine without having to do some form of gravity assist.  You can improve on that dV slightly if you use drop tanks and discard them when empty to keep the weight down.

Never tried this myself so take anything I say with a pinch of salt, but I think I'd probably aim to use Nerv's to get the intercept, and then have an ION powered final stage that does the burns to match speeds with the target and to return.  That way you have a relatively light final stage that only operates in a region where it doesn't get eclipsed very often, meaning it can get most of it's power from solar panels, while the initial boost, where there's a good chance of spending time in Kerbin's shadow, isn't dependant on electricity.

Edited January 15, 2020 by RizzoTheRat

[Mars-Bound Hokie]

3 hours ago, RizzoTheRat said:

The former would be nice but I'm guessing it's the latter.

My thoughts exactly.

 

3 hours ago, RizzoTheRat said:

If my maths is right (big disclaimer :D) Haycals orbit has a period of 6.5 years, meaning you don't really get a lot of choice where you intercept

According to my MATLAB script, you are correct.

• I entered Haycal's apoapsis and periapsis altitude in the command window. It then calculated her orbital period around the sun.
  • Although the program assumes that I am entering the stats of a prograde orbit. It probably doesn't make a difference.

 

 

Here's my craft right now.

• I have 11,473 m/s of dV to spare after going in a retrograde solar orbit.
  • I looked online for the minimum safe distance from Kerbol, but the highest I got was ~10 Mm. I think I'm good with a 561 Mm periapsis.
• My plane-changing node is in ~69 days.
• I have monopropellant in case my target can't EVA herself to the capsule.

 

I think I'm good with the power. The engines didn't run out of energy when it was their turn to complete the 180-degree node, and my periapsis will take me very close to the sun. Regardless if the rendezvous autopilot circularizes my orbit at apoapsis or periapsis (before making the intercept burn), I should have a sufficient power intake. 

 

Any red flags I should be aware of?

[RizzoTheRat]

3 hours ago, Mars-Bound Hokie said:

According to my MATLAB script.

Ooo, nice. 

 

3 hours ago, Mars-Bound Hokie said:

Any red flags I should be aware of?

 

I see from earlier post you're on a unmodded game so hopefully you're good.  I did a retrograde mun orbit rescue the other day and when I got there discovered the capsule was a cupola from a mod that didn't have a door 

[Superfluous J]

The most economical way to complete this contract is the big red X in Mission Control.

 

Edited January 15, 2020 by 5thHorseman

[Mars-Bound Hokie]

4 hours ago, 5thHorseman said:

The most economical way to complete this contract is the big red X in Mission Control.

 

Actually, it makes more sense to rescue Haycal since my craft is about 856K and a new hire would cost me 1.342M. Add the contract rewards to the rescued kerbal, and I get a new pilot for almost (less than) half the price of a brand-new one - along with a reputation boost and the chance of another contract.

[Laie]

@Mars-Bound Hokie could you post Haycal's orbital parameters, please? SMA and Eccentricity will do, as I already know the inclination. I'd like to give it a try.

[Superfluous J]

2 hours ago, Mars-Bound Hokie said:

Actually, it makes more sense to rescue Haycal since my craft is about 856K and a new hire would cost me 1.342M. Add the contract rewards to the rescued kerbal, and I get a new pilot for almost (less than) half the price of a brand-new one - along with a reputation boost and the chance of another contract.

Or you could cancel it and rescue someone from LKO instead. You still get the Kerbal and actually profit from the contract.

But really, everybody should rescue someone from retrograde solar at least once in their life, if only to know without a doubt how bad an idea it is.

[AHHans]

10 hours ago, 5thHorseman said:

The most economical way to complete this contract is the big red X in Mission Control.

Well, that's true if you only look at the funds expended vs. funds gained. But if you look at the satisfaction of rescuing a Kerbal in peril vs. the knowledge that you abandoned a fellow astronaut to her (I think) death, or just the satisfaction of getting a really hard mission done, then it's a lot different.

5 hours ago, Laie said:

@Mars-Bound Hokie could you post Haycal's orbital parameters, please?

It's in the first post: AP:  53,476,467,987m; PE: 41,561,681,152m; Inclination: 177 deg.

[Laie]

1 hour ago, AHHans said:

It's in the first post: AP:  53,476,467,987m; PE: 41,561,681,152m; Inclination: 177 deg.

I hoped I could avoid figuring out the eccentricity from the data given... but meanwhile arrived at ~0.12 by sheer trial and error.

Just by the way, solar limbo is a game unto itself. At 2Mm there's no immediate danger to the craft as such, but the yellow face is nibbling our ablators!

Problem only occurs at warp >100 -- but going through the danger zone at low warp would take half an hour on every pass. It helps to orient the vessel such as to reduce insolation (not a typo). I'm not sure if radiators are of any use, but large solar panels are definitely a liability.

A higher solar PE will only cost a couple hundred m/s , perhaps that's the easiest solution.

Edited January 16, 2020 by Laie

[Laie]

On 1/14/2020 at 8:46 PM, Mars-Bound Hokie said:

I got sick of people asking about orbital parameters while they're right in front of them.

Calm down, man. My method of arriving at eccentricity is to throw numbers into the "Set orbit" window until it looks about right. Which is neither very fast nor precise. I thought I'd just ask, that's all.

Edited January 17, 2020 by Laie