[EMAIL PROTECTED]: > > [..] > > The road map we've been implicitly following is this: > > > > . LV2 demonstrates telemetry and orienteering > > > > . LV2+ demonstrates trajectory following > > > > . LV3 design phase low cost amateur launch vehicle > > > > . Motor shopping > > > > . LV3 orbital operations > > > > any plan for multi-stage testing?
Presumably LV3 is a 2 or 3 stage vehicle. It's still all very preliminary but i would assume flight testing the upper stage 1st. Possibly flight testing the lower stage separately, Then doing a multi-stage orbital (woo hoo) mission. > > [..] > > Crunched versions of LV2 have demonstrated telemetry and sensor > > package. (Despite the transverse noise i'm not worried about the basic > > IMU design.) > > > > IMNHO we know how to solve the orienteering problem. If we had a > > couple full time graduate slaves we could bang out a solution in a > > couple months. > > how [] will the orienteering problem be solved? Well, this seems like a fair question ;) Nowadays it's almost been reduced to a textbook exercise, but not quite. For an opening paragraph i get to pick buzz words, i think i'll pick "sensor fusion" and "complementary filter". We want the control system to do several things . Follow a prescribed trajectory with multi-meter accuracy . Orient the vehicle with ~degree accuracy . Damp structural instabilities . Respond gracefully to un-programmed events . Respond quickly if appropriate . Be reliable and fault tolerant In addition we want the telemetry to report vehicle orientation with ~meter/~degree accuracy at sub-second rates. I think all these points are defensible, for now i will assume them. Formerly solving a tracking problem like this would involve something like the Goldstone radio antenna or similar infrastructure. These days we have satnav like the GPS. For meter-level accuracy the GPS is sufficient, but has several short comings . Low update rates . High drop-out rate . Does not provide attitude information Actually, all of these problems can be addressed. It's even possible to do a GPS-only sensor package, but it's probably not wise. Rather the approach we've been pursuing is to get the best GPS unit we can, cheaply. That means update rates of ~10Hz, probably no multi-second dropouts, and, at least at 1st, no GPS attitude info. Therefore the GPS is insufficient on several counts . Too slow . Not reliable . No attitude information Maybe i'm being too pedantic here, because these are clearly the reasons why we build the IMU. The IMU has properties that complement the GPS. Specifically . Fast (100's Hz) . Reliable (No outside signals) . Measures complete inertial state The IMU also has the significant problem of drift. After a certain number of seconds position estimates derived from IMU data are inaccurate due to integrated measurement error. The idea then is to use the GPS with meter position accuracy and sub-second un-reliability coupled to the IMU with multi-second accuracy and high, fast precision. Together the two systems are meter/degree accurate, kHz fast, and somewhat fault tolerant. To do the actual sensor coupling we are currently pushing two different approaches. The more conventional approach is the extended Kalman filter (EKF) which basically does a least-squares estimate on a linearized state-space model. The other tack is a Bayesian particle filter (BPF). This is a Monte Carlo method operating in real time on a system model that does not necessarily need to be linearized. There is a trade off between the number of sensor inputs, reliability, and computational burden. So far we have generally chosen to pursue sensors which are cheap and orthogonal. Here are our favorites in semi-order . GPS . accelerometer / rate gyro (aka IMU) . pressure . magnetometer . temperature . airspeed . telemetry Doppler . other radio nav . active radar . star sensor . camera vision I'm probably forgetting some, we really should have a list somewhere. Anyone care to add? Currently we're planning to use everything from magnetometer upward on LV2c. _______________________________________________ psas-avionics mailing list psas-avionics@lists.psas.pdx.edu http://lists.psas.pdx.edu/mailman/listinfo/psas-avionics
