Mission To Mars In Kerbal Space Program, Where distances are 1/9 real world values

Things to know about orbital mechanics and space To increase altitude at one point in orbit, the orbiting object must increase its velocity (burn prograde) 180 degrees from the point, slow (burn retrograde) to decrease altitude Extremes in orbital altitude are call Apsis An orbit high point is called Apogee when orbiting earth or one of its satellites, Apoapsis when concerning any other body. Low points are Perigee and Periapsis for Earth and any other body, Respectively

Cont. An orbit with a lower perigee and apogee than another orbit will orbit quicker (smaller orbital period) If two orbits have the same apoapsis or periapsis, but not both, the orbit with the lower non-shared apsis will have a smaller orbital period. Orbital period is independent of orbital inclination

Gravity slingshot Image you are approaching a sharp, 180 degree turn in the road at velocity v. When you enter the turn, centrifugal force in the form of friction accelerates you. You’re speed remains constant, but your direction has flipped! In terms of delta-v, this is 2v.

Cont. Now imagine you are approaching a planet. The same 180 degree turn occurs, but gravity does all the work! You just got 2v delta-v for free! You don’t always get 2v delta v, and you don’t always turn 180 degrees. It depends on how you approach a body. This highly efficient method is employed by space agencies around the world. It allows objects to go to planets around the solar system on small rockets. An example being the MAVEN probe on the Atlas-V rocket.

Specific Impulse Specific Impulse (seconds) measures an engines efficiency. It is given by this equation Isp= Thrust/(Fuel Consumption per second) If one simplifies N/(kg/s), they are left with seconds. Similar to how power and torque are both kg-meters, time seconds and Isp seconds do not measure the same thing. High specific impulse engines are usually very efficient, but do not provide much thrust. High thrust engines are not usually powerful

Cont. Real world examples: The Rocketdyne F-1 engine powered the Saturn-V Apollo rocket, its Isp was only 263 seconds, but it packed a 6.77 Mega- Newton punch! The NEXT ion thruster only provides 246 milli- newtons of thrust, but has an Isp of 4,300 seconds. The F-1 is ideal for moving a lot into orbit quickly when efficiency isn’t a big concern. The NEXT is ideal for small, light, efficient spacecraft on multi- decade long missions

The Ship

Ship Characteristics 1500 kN 1 st stage, with an additional 6 boosters with 1500 kN each. Average specific impulse of Interplanetary stage with two 60 kN engines. Average Isp of 800. (These are called NERVA engines- they use nuclear fission to heat exhaust particles for extra efficiency) 1 Landing stage with four 50 kN engines, with an average Isp of 390

Ship notes As gravity and air resistance decrease with altitude, the need for thrust diminishes. To capitalize with this boosters on the launch vehicle and lander are staggered in separation, with one pair discarding at a time High thrust engines used for launcher and lander Highly efficient engines used for interplanetary stage The lander has a crazy number of parachutes due to the thin Martian air, this would not work in reality. NASA used a rocket powered “skycrane” to lower its most recent rover. Very similar mission profile to the Apollo missions in regards to the lander docking

Launch

1 st booster pair sep

2 nd booster pair sep. Ship begins orbital insertion turn

3 rd Booster sep. Most of the thrust now going horizontal

Target apogee of 75km reached, main engine shut off

Ship burns prograde at apogee to raise perigee

Orbit circularized

Earth departure burn

Departure burn was aimed to increase velocity with Earth’s orbit This raised the apoapsis to match Mars and exited Earth in one burn!

After 1 st stage separation Downward burn to align with Martian orbital inclination

Prograde burn at Apoapsis to encounter Mars on next orbit

Hello Mars! Retrograde burn to match Martian velocity and enter Martian orbit

Retrograde burn at Periapsis to circularize orbit

Lander Separation and retrograde burn to slow at apoapsis to enter Martion atmosphere

Atmospheric drag on lander and parachute bundle provides free delta-v

Lander uses almost no fuel to land (landing gear sunk into surface)

One small step…

Lander taking off to rendezvous with interplanetary stage

1 st booster sep.

Apoapsides matched, periapsis left lower so lander can catch up to target

Lander and Interplanetary-Stage meet

And dock

Lander boosters separated to reduce mass

Burning prograde to depart Mars

Gravity assist from a Martian moon to depart Mars free delta-v!

Downward burn to match Earth’s orbital inclination

Burning retrograde at apoapsis to match Earth at periapsis

Approaching earth

Home Sweet Home! (Earth intercept lead to a direct insertion, no burns needed)

Mission Notes Duration 606 days, 11 hours, 15 minutes and 42 seconds in game. Rocket design and mission took about 3 hours in real time. Launch stage ended up on orbit with over 1000 m/s delta-v left over. This stage could be trimmed down Interplanetary stage used less than 1/3 of total fuel. This stage could be made much smaller, and perhaps be cut down to one engine. Lander legs appeared to fail on landing, a short burn before landing should be added to mission profile Gravity assists from moons to exit Earth orbit and enter Martian orbit should be considered. Estimate total mission efficiency at ~40%