Suborbital Strike

[sevenperforce]

I've always loved the Nike Sprint ABM, with its ridiculous 100G acceleration and boost-phase skin temperatures rivaling re-entry energies. It was a marvel of rocket science and advanced engineering. Unfortunately, there isn't much of a way to introduce a high-acceleration ballistic interceptor into KSP challenges. You can replicate it, of course, but it's not really good for anything. There have been challenges where you try to get a rocket as close as possible to an orbiting target, but that takes a lot of effort and doesn't really play into design as much as dumb luck. But I thought of a challenge that might push people to design an ICBM-style vehicle, so here you go.

Long-awaited funding for the Kartemis Missions has finally come through, and the VAB is due for a much-needed upgrade. An upgrade, of course, first requires a demolition, so the KSP agrees to build one final VAB rocket to get the job done. Ordinarily, a ballistic missile would carry a warhead, but to avoid damage to the surrounding buildings the impactor will be purely kinetic. The launch will also have a liftoff limit of 120 tonnes.

Because the KSP complex will be evacuated for safety during the mission, the Deep Space Kerbnet will be shut down. Accordingly, all engine burns must take place before entering the upper atmosphere. The impactor must stay below 150 km altitude for its targeting systems to remain functional.

Your mission is to destroy the VAB with a suborbital ballistic impactor. The impactor with the greatest kinetic energy (if you don't know how to calculate kinetic energy, Google it) wins, provided that your launch vehicle was less than 120 tonnes at liftoff, launch clamps and other ground assets excluded. No engine burn may be conducted after crossing 35 km altitude; your impactor cannot exceed 150 km altitude at any time.

Because the KSP physics engine handles high-velocity impacts poorly, it is not necessary that the VAB actually be leveled; it is enough that your impactor strike the ground reasonably close to the VAB. Your score is your calculated kinetic energy at impact, modified by the following bonuses:

• Pinpoint Precision: Actually level the VAB. +3%.
• Sprint Style: Two-stage solid-fueled vehicle with liquid verniers on the first stage and no RCS. +5%.
• Super Sprint: Engine burnout below 15 km. +10%.
• GNOM Style: Ramjet boost stage launched from a mobile, wheeled platform. +5%.
• Accidental Elon: Single-stage liquid rocket which impacts engine-first and steers descent using fold-out fins, like a returning Falcon Heavy booster. +8%.
• Poseidon Style: Two-stage solid-fueled missile with vernier guidance on both stages, launched from underwater. Upper stage uses RCS once exoatmospheric for guidance, then releases a purely ballistic, unguided impactor. +12%.
• Pootin' Style: Final stage may fire engines within atmosphere up until impact, subject to the following limitations (+30%):
  • Final/cruise stage may only carry Whiplash engines with infinite fuel enabled and can only ignite after re-entry
  • Must launch vertically from either the Desert Airfield or Woomerang
  • Max altitude limited to 100 km
  • Kinetic energy calculation may only use mass of onboard RTGs at impact
• Kamikaze: Your launch vehicle will be crewed and otherwise unguided; the Kerbal must bail out (and survive) no more than 5 km in altitude, just before impact. (+20%).
• Kim Jung Boom Style: Single-stage liquid-fueled launch vehicle with a fixed main engine and four verniers; upper stage uses RCS once exoatmospheric for guidance, then releases a purely ballistic, unguided impactor. +10%.
• Von Braun Style: Single-stage liquid-fueled ogive missile with fixed external fins, like a V-2. Entire rocket must remain in one piece until impact. +6%.

Good luck!

[ralanboyle]

Questions: 

1. Do we have to go above 35km? 

2. If we go above 35km, are targeting burns allowed once back below 35km? 

3. Is there a specific airfield we are supposed to use? 

4. Is something like the Bastion Coastal Defense Missile acceptable?

     Exhibit A: 

 

Edited April 5, 2020 by ralanboyle
Edit

[sevenperforce]

3 hours ago, ralanboyle said:

Questions: 

1. Do we have to go above 35km? 

Yes, you have to go into suborbital spaceflight. So, a boost stage (or stages) that burn out under 35 km to put you onto a suborbital trajectory above 70 km. Realistically you will need to have an apoapsis at burnout well over 70 km in order to actually make it into space when coasting from 35 km.

3 hours ago, ralanboyle said:

2. If we go above 35km, are targeting burns allowed once back below 35km? 

I expect people will use RCS to adjust trajectory, then a ballistic re-entry. You cannot use your main engine, though. Correction burns after crossing 35 km are fine as long as they do not use the main engine or add appreciably to the missile's kinetic energy. The point of the 35 km burn ceiling for a suborbital missile is to push people toward high-acceleration ICBMs that produce as much thrust early on as possible and involve a significant ballistic element.

3 hours ago, ralanboyle said:

3. Is there a specific airfield we are supposed to use? 

I also expect that most people will merely launch straight up from the pad at the KSC, pitch just slightly downrange, then fall back straight down. That's easiest, and it lets people focus on their rocket design rather than spending endless hours figuring out how to target KSC from the desert airfield or elsewhere.

3 hours ago, ralanboyle said:

4. Is something like the Bastion Coastal Defense Missile acceptable?

     Exhibit A...

Nope -- it needs to go into space and then fall back down without thrust until impact. 

[ralanboyle]

Okay,

Here is my Pootin Style ICBM.  

The cruise stage empty weight is 3680, and it impacts the VAB at 1103 m/s so the energy is 4,059,040. 

Pootin Style adds a 30% multiplier, that makes the final score 5,276,752.