# Nano spacecraft reentry

Suppose if one designs a Small size reentry capsule. What will be the typical deacceleration achieved by atmosphere. More precisely, what is the relationship of the size and drag by atmosphere.

I am trying to see feasibility of soft landing by a small spacecraft.

• Sample return missions have attempted and will continue to attempt relatively soft landings and there has been some success, so feasibility is not in question. You might consider asking a second question about that, asking for a few examples and/or if any were as small as a cubesat. – uhoh Mar 24 '18 at 4:49
• Indeed, Iam aware of it has been attempted in many asteroid sample return missions. Most important factor is deacceleration one can achieve. Mass of about 10-15 kgs and diameter of heat shield of about > 50 cm and < 100 cm. Now in this constraint, one can probably aim for small cold thrusters for breaking just before touchdown just like soyuz. And small parachute too probably. But what would be terminal velocity of such capsule? Will it be more compared to big spacecraft or less? – Prakhar Mar 24 '18 at 5:19
• $D=\rho v^2C_dA$, where the atmospheric density can be estimated by $\rho\approx \rho_0e^{-\frac{h}{h_0}}$, where h is the altitude above sea level – Paul Mar 24 '18 at 21:15
• Are you asking about landing or the reentry deceleration? Small bodies tend to have small mass-to-area ratios, which make for high deceleration and high instantaneous heat flux. It’s very hard to make those numbers work for a CubeSat-sized vehicle. – Bob Jacobsen Mar 24 '18 at 23:37
• Very hard, because of heat? What are the challenges exactly ? – Prakhar Mar 25 '18 at 3:18