Fastest Kerbin Circumnavigation

[Zeroignite]

New Challenge here! How fast can you complete one lap around Kerbin?

Using a completely boring MechJeb ascent path and parachute landing, a full orbit of Kerbin takes about 39 minutes.

We're Kerbonauts. We can do better. What does it take, in terms of piloting, rocket design, and creativity to reduce that time?

RULES:

"Circumnavigation" consists of taking off from either the runway or the launchpad, going completely around Kerbin, and landing on the KSC terrain (the brownish, flat grassy area).

The vessel must contain a crew member, and that crew member must be alive on landing. There is no requirement for landing intact.

A valid submission consists of an image of the Flight Results screen [F3] taken upon landing, plus mod notes below. Photos of the mission and launch vehicles are nice but not required.

MODS:

I don't want to enforce any strict mod requirements. Similar to the old Bobcat Colonization Challenge, feel free to use whatever you feel is reasonably balanced against stock. However, there will be a few different categories since some people want to play purely stock, and scoring that alongside mod parts might be considered unfair.

Please declare what mods you're running for your challenge submission.

Leaderboard categories are:

Purist (no mods except background plugins/navigational aids or mods that make the game objectively harder);

Extended (full part mods, but again try to keep things balanced against stock);

FAR (any entry with Ferram Aerodynamics Research enabled, since that drastically changes the drag model).

LEADERBOARDS

Purist:

1: 23:03 zarakon --- (Rocket, LV-N cruise, orbit west) [Flight Engineer]

2: 35:31 SaturnVee --- (Rocket) [sTOCK]

3: 35:37 Cal'Mihe --- (Jet w/ LV-N cruise) [Flight Engineer]

4: 37:04 Octagon --- (Jet) [sTOCK]

5: 37:24 Zeroignite --- (Rocket) [MechJeb, Deadly Reentry]

Extended:

1: 35:28 joshblake --- (Jet, SRB assist takeoff) [MechJeb, Procedural Wings, Fuel Balancer]

FAR:

1: [MET] [username] --- [relevant mods]

SPECIAL:

numberosis in 11:40 using inf fuel as a mathematical proof-of-concept.

I'm really looking forward to seeing what people come up with to shave off MET. You'll need to pack a lot of delta-v above and beyond what's required to get into orbit. I am also really curious to see if any high-altitude superjets can contend, since there are some of those which can exceed orbital velocity.

Edited August 17, 2013 by Zeroignite
leaderboard update

[Zeroignite]

Here's my submission

MET: 37:24

MODS: MechJeb (Bill 9000 part), Deadly Reentry

My approach here was to use a high TWR launch vehicle into a 70km orbit, not limiting myself to any kind of efficient ascent. Orbit was pure ballistic eastward, no shenanigans there. For descent, I did a steep deorbit burn, then thrusted downward/forward to get through the atmosphere faster while still hitting KSC. Deadly Reentry did me no favors on either ascent or reentry, since I had to limit acceleration on the former, and some of my parts burned up on the latter. In the end I was aiming for a powered descent w/ parachute for retrograde-pointing and an extra layer of safety. Most of the ship burned up on reentry, including the parachute and two of the landing legs. In the end I lithobraked pretty hard at the end of my descent burn, but was slow enough and had enough fueltank crumple zone for the capsule to survive. Good enough

[Octagon]

My entry:

MET: 37:04

MODS: No Mods, pure skill.

No rocket engines, only jet. I will post a faster plane later.

Edited August 14, 2013 by Octagon

[Zeroignite]

Well done, Octagon! What kind of cruise altitude did you get, and how many engines are stuffed into the back?

Added to leaderboard.

[zarakon]

I've got a rocket that can do it in under 25 minutes... but then actually landing at KSC is rather difficult

[Van Disaster]

Was on course for ~30min in an aircraft ( with FAR ), but got a bit violent right in sight of the runway & spun :S. Another go later.

[Octagon]

Well done, Octagon! What kind of cruise altitude did you get, and how many engines are stuffed into the back?

Added to leaderboard.

Thank you Zeroignite. To accomplish the task, I used only one engine. The trick is to fly at high altitudes (in this case +-33000 meters) keeping the engine at less then a third, so this is also an economic way to circumnavigate. I'm now working on a plane capable of flying at +-41000 meters and 2300m/s. Rocket-assisted take-off is good way to start, although I haven't used it.

[Cal'Mihe]

Reposting this from the old tread back on page 8 which died before it was properly recognized

Vessel : AF-2W Starspeeder

Pilot: Merrie Kerman

All parts stock (only mod is Kerbal engineer),

Touched down at 35:06 and came to a stop at: 35 minutes and 37 seconds

That old challenge had an altitude limit of 45km, so I had to stay below that, it could undoubtably be done faster at 55km or higher, but then you'd spend the vast majority of fuel and dV trusting downwards to avoid scooting off into interplanetary space

The hard part is when to start comming down from 43k meters without overshooting and losing time that way Most of the cruising is done at 42k and at 2450 m/s, with the nose pointing straight down, to keep speed above orbital ejection velocities, but still remain below the 45k.

I had a try yesterday that could go to 2550 m/s, but sadly I had messed up the weight balancing when empty, and it spun out and lost control just as I overshot KSC on comming back.

Reaching cruising position:

Cruising position, trusting down to maintain speed and altitude

The fireworks as we come down towards KSC with full power to the jet engines (I had too much jet fuel left)

Getting Mach effects comming down fast towards the runway:

Approaching runway:

Mission log at End of flight:

Apparently I bumped down just a tad faster than usual, as I had one of the engines come loose while touching down, then jiggling around as I rolled off the runway.

A shot of the bird in the hangar:

[maltesh]

This is one of those situations where you can probably shave some time off your attempt by heading West. The rotation of Kerbin will carry KSC over 300km eastward in the 35-ish minutes it takes you to throw your aerospacecraft around the planet.

[SaturnVee]

Just about got 35:30

No mods, went for an incredibly early gravity turn west and held a 70k orbit until I planned a descent onto KSC.

Perfect landing

And the ship that did it

Edited August 16, 2013 by SaturnVee

[numerobis]

What you gain in Kerbin's rotation you lose in extra deltaV requirement, no?

[zarakon]

What you gain in Kerbin's rotation you lose in extra deltaV requirement, no?

It takes you about 350 m/s more delta V and a little bit more time to get into orbit

But in this challenge it is worth it because in a westward orbit your surface speed will be about 350 m/s higher for the same orbital speed and altitude, compared to an eastward orbit. You'll complete your circumnavigation sooner.

It's not easy to make up for it by simply going 350 m/s faster, because that would greatly increase how much you spend afterward, burning toward the surface to maintain a low altitude

For a jet plane it doesn't matter as much since you're limited by air speed (same as surface speed) anyway. At very high speeds though, flying east can make it difficult to stay in the atmosphere, since your orbital velocity can get very high (175 above your air speed). Going west, you'll never have to worry about accidentally flying into orbit, but you'll have to work harder to maintain altitude.

Edited August 15, 2013 by zarakon

[Zeroignite]

Vessel : AF-2W Starspeeder

Pilot: Merrie Kerman

All parts stock (only mod is Kerbal engineer)' date='

[/quote']Dang, well done! Welcome to leaderboard #1.

maltesh: Yeah, I've been thinking about doing a westward flight, but haven't implemented it yet or done the math to see if it'd be worthwhile. Probably better to do as a VAB launch so you don't waste time turning to heading 270.

[Octagon]

Dang, well done! Welcome to leaderboard #1.

maltesh: Yeah, I've been thinking about doing a westward flight, but haven't implemented it yet or done the math to see if it'd be worthwhile. Probably better to do as a VAB launch so you don't waste time turning to heading 270.

Do a loop! You will expend the time that will be used to gain altitude. I tried it and, as Zarakon said: Is hard to keep high altitudes. To the conventional side, the plane flies like a plume.

[maltesh]

You could also use the old trick of making your plane face in the opposite direction in the SPH...Except there are those lights in the way now.

[zarakon]

23:03

Rocket, stock+engineer

(Click for full-size images)

[Zeroignite]

I love the forums, always pushing things to beyond what looks possible S'part of why I tossed down this challenge.

Welcome to #1, Zakaron.

[joshblake]

Here is my submission:

MET: 35:28

Mods used: Mechjeb, Engineer, proc wings, TAC fuel balancer.

Approach: A superjet named HyperLily II.

Specs:

• 36 ram air intakes
  
• 5 Turbojets.
  
• 2 RT-10 solid rocket boosters to assist getting to cruising altitude (10km) quickly, then dropped.
  
• RCS
  
• Mk2 cockpit in "escape pod" configuration: separator and parachute.
  

Pics:

Javascript is disabled. View full album

I messed up the first 1/3 of the cruise trajectory since I let myself get too high before correcting, and my velocity carried me up to about 50 km, starving the engines. I was trying to stay between 30km and 40km. It took me another 1/3 of the flight basically waiting to reach and come back down from apoapsis. This was helped slightly by a -50 degree pitch to increase drag and lower the apoapsis.

Once the engines kicked back in, I re-established a superjet cruising trajectory and held around 31-33km altitude. I had to vary my pitch between +5 and -10 degrees to manage my vertical velocity, as my apoapsis was 70-80km at that point. I kept my vertical velocity 0 m/s +-20 m/s (which keeps the periapsis near me and the apoapsis constantly moving on the other side of the planet.) Beyond managing vertical velocity, I tried to balance air density so I could have enough air intake to for the engines to accelerate as much as possible but minimize the drag. Peak velocity was approximately 2215 m/s.

Descent started at 230 km from KSC from altitude of 31.5km with a -15 degree pitch most of the way.

Mechjeb Smart A.S.S. Surface hold was critical for this flight. I also used the TAC Fuel Balancer from the beginning so the center-of-balance didn't get all wonky relative to the center-of-lift as we burnt fuel. I kept the Spaceplane Guidance pane open just to track the distance to runway, and use the Landing Guidance pane to judge when to start the descent. Descent was flown using Smart A.S.S. and manually near the end.

I will probably try again with a better trajectory. I could probably shave 1-2 minutes off with this jet. I also had more than enough fuel, although I didn't use as much as normal due to the altitude excursion and jet flameout.

[Zeroignite]

Added to leaderboard

Procedural wings make you the first entry in the "Extended" category.

[numerobis]

I don't actually play this game, I just like doing the math for it. So here goes: you've all convinced me you need to thrust down to win this challenge. So let's calculate how long it takes to go around the world once we get up to speed and are now thrusting straight down.

To stay in a circular trajectory around a center, you need a centripetal force of

a = v_orbit^2 / r
v_orbit = sqrt(r a)

where v is your speed (orbit speed in KSP terms) and r is the radius of your circle. The time it takes to do a full rotation is:

t = 2 pi r / v_surface
t = 2 pi r / (v_orbit - v_rotation * cos(inclination))

This predicts what maltesh was saying (though as zarakon points out, it doesn't work with jets, since their thrust depends on surface speed): for a given orbit speed and infinite fuel, to reduce time, you should fly at inclination 180, aka due West.

Putting it all together, flying West, we get:

v_orbit = sqrt(r a)
t = 2 pi r / (sqrt(r a) + v_rotation)

That predicts you want to fly as low as possible: t grows as the sqrt®. And you want as much thrust as possible.

We get one gravity for free; the rest of the acceleration is going to be rockets:

a = g + thrust / mass

All that in mind, I did actually play the game, but with infinite fuel on. I took a cockpit and added a few parachutes and a mainsail. This puppy gets almost 200 m/s^2 of thrust, to which we add 7.9 for gravity at the top of the atmosphere. The math predicts that circumnavigating should take:

r = 670000 m
a = 207 m/s^2
v_rotation = 175 m/s
v_orbit = 11777 m/s
t = 352 s

So I flew that: full thrust; vertical until apoapsis hit 20km, then quickly level out with heading 270, accelerate until 11.5 km/s orbit speed, then quickly to -90 pitch. Landing was a matter of, about 30 degrees east of KSC, doing a retro burn until MechJeb predicted an arrival at KSC, then burning directly towards KSC; I didn't optimize the landing much. At 500m altitude, going nearly 1km/s, I pulled up, staged the mainsail off, and let out the parachutes. So I have about two minutes of floating down on my time -- compare my MET to the time at which the mainsail landed, which was only a second or so after dropping it. Also, I porpoised from 70 km to 140 km during my orbit. All in all, the math appears to be pretty close.

MET: 11m40s, mechjeb, infinite fuel

Now I just need to design a spacecraft with 100 km/s of deltaV using mainsails.

Edited August 16, 2013 by numerobis

[glacierre]

I don't actually play this game, I just like doing the math for it.

That's golden!

[zarakon]

Now I just need to design a spacecraft with 100 km/s of deltaV using mainsails.

and a sustained T:W ratio around 20:1

good luck!

I was wondering if, for a given amount of thrust, flying higher might actually be advantageous. You have a longer distance to travel, but you can also maintain a higher speed. But your math does show that lower is better!

Edited August 16, 2013 by zarakon

[Zeroignite]

SaturnVee, sorry for missing your post --- added to leaderboard

numberosis, I've added you to the OP as a special proof-of-concept.

EDIT: If I miss a submission, please PM me! Sometimes it seems I load threads in the wrong place.

[zarakon]

SaturnVee, sorry for missing your post --- added to leaderboard

His time was 35:31, but you listed it as 25:30

[SaturnVee]

SaturnVee, sorry for missing your post --- added to leaderboard

numberosis, I've added you to the OP as a special proof-of-concept.

EDIT: If I miss a submission, please PM me! Sometimes it seems I load threads in the wrong place.

No problem , it appeared there because I posted it quite early, but moderators only approved my message quite a bit later.