Open Access

Jan Thimo Grundmann, Wlademar Bauer, Kai Borchers, Etienne Dumont, Christian D. Grimm, Tra-Mi Ho, Rico Jahnke, Aaron D. Koch, Caroline Lange, Volker Maiwald, Jan-Gerd Meß, Eugen Mikulz, Dominik Quantius, Siebo Reershemius, Thomas Renger, Kaname Sasaki, Patric Seefeldt, Peter Spietz, Tom Spröwitz, Maciej Sznajder, Norbert Toth, Matteo Ceriotti, Colin McInnes, Alessandro Peloni, Jens Biele, Christian Krause, Bernd Dachwald, David Hercik, Roy Lichtenheldt, Friederike Wolff, Alexander Koncz, Ivanka Pelivan, Nicole Schmitz, Ralf Boden, Johannes Riemann, Wolfgang Seboldt, Elisabet Wejmo, Christian Ziach, Tobias Mikschl, Sergio Montenegro, Michael Ruffer, Federico Cordero, Simon Tardivel

• 20 years after the successful ground deployment test of a (20 m) 2 solar sail at DLR Cologne, and in the light of the upcoming U.S. NEAscout mission, we provide an overview of the progress made since in our mission and hardware design studies as well as the hardware built in the course of our solar sail technology development. We outline the most likely and most efficient routes to develop solar sails for useful missions in science and applications, based on our developed `now-term' and near-term hardware as well as the many practical and managerial lessons learned from the DLR-ESTEC Gossamer Roadmap. Mission types directly applicable to planetary defense include single and Multiple NEA Rendezvous ((M)NR) for precursor, monitoring and follow-up scenarios as well as sail-propelled head-on retrograde kinetic impactors (RKI) for mitigation. Other mission types such as the Displaced L1 (DL1) space weather advance warning and monitoring or Solar Polar Orbiter (SPO) types demonstrate the capability of near-term solar sails to achieve asteroid rendezvous in any kind of orbit, from Earth-coorbital to extremely inclined and even retrograde orbits. Some of these mission types such as SPO, (M)NR and RKI include separable payloads. For one-way access to the asteroid surface, nanolanders like MASCOT are an ideal match for solar sails in micro-spacecraft format, i.e. in launch configurations compatible with ESPA and ASAP secondary payload platforms. Larger landers similar to the JAXA-DLR study of a Jupiter Trojan asteroid lander for the OKEANOS mission can shuttle from the sail to the asteroids visited and enable multiple NEA sample-return missions. The high impact velocities and re-try capability achieved by the RKI mission type on a final orbit identical to the target asteroid's but retrograde to its motion enables small spacecraft size impactors to carry sufficient kinetic energy for deflection.