Last November 16, REXUS 11 was finally launched from Esrange, and with it the RAIN experiment. The launch was a success, not only for REXUS 11 in general, but also for the RAIN experiment. Last Tuesday the RAIN team flew back from Kiruna to Stockholm, and yesterday they gave a very interesting presentation at KTH about the launch campaign and some of the results that they obtained. Naturally most of what was collected still needs to be analyzed, but there are already some things that we can learn from RAIN’s successful launch.
For example, one thing that we can learn is related to the ejection moment itself. Upon ejection, the FFUs’ spin rate was reduced significantly due to friction, from 3.4 Hz to 1.6 Hz. A similar effect could be expected for our case as well. Also, the spinning ejection test that is supposed to be performed soon will for sure tell us more about this as well.
During the whole flight, the RAIN FFUs recorded raw GPS data and internal data, allowing to reconstruct position, velocity and acceleration for all the phases of flight. For the MUSCAT experiment, it is absolutely essencial that good data is obtained for these variables, since they will allow to derive the density and temperature profiles in the middle atmosphere. Therefore, we are especially glad that this worked out so well for them, and hope the same goes for us. In the case of RAIN, it is not possible to derive the density and temperature profiles from this data because there is also the need to have an accurate value of the drag coefficient for several Mach and Reynolds numbers. Because the RAIN FFUs are cylindrical, this is hard to obtain for them; however, the spherical shape of the MUSCAT FFUs has precisely the objective of allowing an estimation of the drag coefficient to derive these profiles.
Finally, we were also glad to know that the FFUs were recovered in only 30 minutes (take a look at some recovery photos here). Both the GPS commercial data and the modulation into a beacon signal worked out pretty well. In the meantime, the MUSCAT team will have to guaratee that this will work without failures for us too, since we need to recover 3 out of the 4 FFUs for the experiment to be a success!