In the book Delta-V, a climactic scene involves a high-acceleration return from the orbit of Ryugu to Earth. The book makes a big deal about the delta-v needed for the trajectory (hence the name) so I was curious how realistic the scenario is. Here's what gets presented:
- They are initially in Ryugu's orbit (Aphelion 1.4159 AU, Perihelion 0.9633 AU).
- They are delayed and depart a few weeks after the ideal transfer orbit.
- As a result, 24.42 km/s of delta-v are needed to intersect Earth's orbit.
- They reach Earth going 26.8 km/s.
- They use aerobreaking to shed 14 km/s and enter an elliptical orbit around Earth.
I would normally trust Suarez to use real orbital mechanics in his books. However, I was a bit suspicious that the ∆v to change orbit and the velocity at Earth were so close. Is this correct, or did Suarez fail to correct for gravitational acceleration during the journey?
Edit. I found some more information about the orbits which might provide info about the position of Ryugu relative to earth for this.
- Their outward trajectory from lunar orbit to Ryugu takes 48 days and requires ∆v = 1.7 km/s plus a postinjection burn of 1.9 km/s. It is dated Dec 13, 2033 to Jan 30, 2034.
- Closest approach for the return orbit occurs in May 2038 at 5.5e7 km
- Return was scheduled for Feb 10, 2038, but they actually left Feb 19.
- Rendezvous occurred around Mar 31, 2038
- A slow trajectory was possible Oct 2, 2036 arriving Jan 2038 (perhaps using gravity assists) using ∆v = 706 m/s
The more I look back at the hard numbers in this book the more I'm inclined to trust Suarez's calculations. I'd still be interested in the math behind them though.