Difference between revisions of "Tutorial:Returning From Eve"

Revision as of 19:34, 6 April 2014

Because of the extreme difficulty concerning any return attempt from Eve, I have decided to write a separate tutorial.

Returning from Eve

Despite being the closest planet relative to Kerbin, it is extremely difficult to get a lander back into orbit around Eve. Additionally, you must overcome Eve's large gravity well in order to successfully return home, requiring even more Delta-V. As a result, many Kerbals have been lost in attempts to investigate their distant neighbor.

Though getting your crew home from the surface of Eve is extremely difficult, it's not impossible.

Specifications

• Length: 1-3 hours
• Difficulty: Very Hard
• For version: 0.20

Additionally, you will need a good understanding of orbital mechanics (see Tutorials section), angles, and a lot of patience. Some knowledge about aerobraking and Advanced Rocket Design might also be useful. Ships described below don't feature lauch vehicle, so any experience in building them is desired.

Method 1 : Rendezvous and Crew Transfer

Mission profile

It's a kind of interplanetary expedition rather than a simple round trip. In my opinion the easiest way is to send lander without crew and return rocket with 2 Kerbals. They'll meet for the first time in Eve orbit, then one daring pilot will take seat in the lander and fly a historic mission!

Designing your Landing Rocket

Ascent rocket will use asparagus staging (see Tutorials) with Upper and Middle Stage in a core and multiple Booster stages grouped in pairs.

Tutorial's example rocket including probe and some electiricty equipment

Upper Stage

This stage has to get above the atmosphere and accelerate itself to orbital velocity. It's important to keep it as lightweight as possible. First choose is a command pod. The best idea is to put single Kerbal in a EAS-1 External Command Seat. Next (but much worse) would be Mk1 Lander Can. I recommend first option and a following stage design:

• EAS-1 External Command Seat
• Inline Advanced Stabilizer // not necessary if you feel confident in piloting
• FL-T400 Fuel Tank
• LV-909 Liquid Fuel Engine

Middle Stage

This stage will propel the ship through middle atmosphere (20km-35km). It's engine should be activated with all lower stage boosters and fed from their tanks:

• TR-18A Stack Decoupler
• FL-T800 Fuel Tank
• LV-T45 Liquid Fuel Engine

Booster Stages

There are two possible ways to build them. One is to use 2xFL-T800 Fuel Tank and LV-T30 Liquid Fuel Engine. Second is: FL-T400 Fuel Tank, FL-T800 Fuel Tank and Toroidal Aerospike Rocket. They have very similar performance but I think aerospikes are better because they lower ship's drag coefficient. The basic rocket will have 3 pairs of aerospike boosters attached around the core stack.

Additional Equipment

You may also need parachutes and landing gear.

• To save weight you can put LT-2 Landing Strut on a TT-38K Radial Decoupler.
• You may need Mk25 Parachute and it's best to put them on top of the boosters.
• For touchdown I used 24 Mk2-R Radial-Mount Parachute mounted on 12 TT-38K Radial Decoupler, two on each booster.
• Don't forget the ladder and some electric gear!

If you want to send lander alone to Eve, add somewhere a probe.

Designing Transfer Vehicle

Although it's not very challenging to send the lander in one launch, it may be easier to split ship into two parts. First will be the lander itself with decoupler below the center engine and Clamp-O-Tron Sr. Docking Port (remember about struts). The second could be simple Rockomax Jumbo-64 Fuel Tank and a couple of (for example 4) nuclear engines with this big docking port on top. Last thing to do is to launch them into Kerbin orbit, then dock and send to Eve. To dock together they'll of course need some RCS.

Designing your Return Rocket

Assuming that we sent ascent rocket alone the return rocket could be as simple as this:

• Mk16-XL Parachute
• Mk2 Lander-can
• TR-XL Stack Separator
• Advanced S.A.S Module, Large
• Rockomax X200-16 Fuel Tank
• LV-N Atomic Rocket Motor

Such rocket has Delta-V of almost 6km/s which is enough for departing Kerbin's orbit, Eve capture, rendezvous with ascent ship and then return to Kerbin.

Landing on Eve

Example lander has Delta-V of about 11km/s. Now it's all depends on the landing site elevation (the higher the better). To find suitable place you can use http://www.kerbalmaps.com/ or send earlier some scout probes or even better - a rover. With this type of design, to calculate needed Delta-V you can use results from my tests:

• 9500m/s from 4,7km elevation
• 10000m/s from 3.9km elevation
• 10700m/s from 3km elevation

That leads to inaccurate rule of thumb that every 1km lower, adds 700m/s to the needed velocity change. Although I managed to return from 555m above sea level having 11.3km/s (with different design), with only 3 pairs of boosters we should not land below 3km, just for safety.

• Note that adding another 3 pairs can bring landing site to below 1km at the expense of complicated design.

Once you got in stable orbit around Eve you can meet with return ship and transfer a pilot to the lander (via EVA). Then using transfer stage deorbit the lander to chosen landing site and then detach it. During descent get rid of the bottom docking port (if used). When below 20km open first pack of chutes - the Mk25_Parachute. To reduce stress wait until 'Drogue' chutes full deploy, and then open first half of radial chutes. Once they deploy at 500m open the rest. If it seems you'll land faster than about 6-8m/s you can make slight burn prior to the touchdown. When on the surface you can detach all those parachutes.

Ascending from Eve

Before attepmting to takeoff - a quicksave.
Now throttle up to 100%, detach landing gear, and as-quick-as-you-can point the rocket straight upwards and turn on SAS. If failed to do so, rocket sooner or later will flip. This will also happen if you try to move it before dropping all those boosters. Only things now are to drop spent stages and maybe control your velocity trying not to exceed terminal velocity (see Eve#Atmosphere).
Start your gravity turn between 30 and 35km with ~70deg of pitch - at this time ship should be running out of fuel in the Middle Stage. When your apoapsis'll raise above 80km you can pitch down to ~20deg and keep looking both on fuel and apoapsis.
Once having apoapsis above the atmosphere (~100km), cutoff the engine and plan manouver to circularize orbit.

Rendezvous with Recovery Vehicle

Now if you managed to return from Eve surface rendezvous should be piece of cake. You can either adjust return ship's orbit to make a rendezvous or fly with the lander (if you have some fuel left). When the distance falls below 1km or less, you can EVA the lander pilot to return ship (after bringing relative velocity near to 0).

Interplanetary Transfer back to Kerbin

Delta-V needed for returning to Kerbin is:

• ~1400m/s - departure from 100km orbit
• ~400m/s - worst case plane change

So exactly 1800m/s would be suitable (the presented return rocket have much more). Calculations are accurate when planets are properly aligned - Kerbin should be aboud 36 degree ahead of Eve (for details see http://ksp.olex.biz/).
After ~42 days, the most daring adventure will end up with reentry and safe splashdown.

Technical notes

• If you decided to use Mk1 Lander Can as a pod in this example rocket, note that safe landing elevation raises to 4,5km (with 3 pairs of boosters) and ~2,3km (with 6 pairs).
• If using more than 3 pairs of boosters, 24 parachutes may not be enough. Also Transfer Stage may became too weak.

Method 2 : Single Rocket Landing and Return

Mission Profile

This could be called 'direct ascent'. Although much more complicated, it's possible. After all, it's all the matter of how many hardware can we bring down to Eve's surface.

Rocket Design

You can use rocket from first method. Now you would use Mk1 Lander Can with parachute on top and the Upper Stage must have 1800m/s left after the ascent. That means lander should use 6 pairs of boosters, and this allow for landing about 5km above sea level.

Special Considerations

It may be tempting to use PB-ION Electric Propulsion System since it's far more efficient and solar panels produce more energy on Eve. But the ejection burn will occur on the night side and could last about an hour.

Further Goals

• Consider sending a rover and use it as a moving base on the surface. You could then land on the hills and drove down to the coastline