dc y trajectory simulation i ve been to three talks in the last month which might be of interest i ve transcribed some of my notes below since my note taking ability is by no means infallible please assume that all factual errors are mine permission is granted to copy this without restriction note for newbies the delta clipper project is geared towards producing a single staget to orbit reusable launch vehicle the dc x vehicle is a scale vehicle designed to test some of the concepts invovled in ssto it is currently undergoing tests the dc y vehicle would be a full scale experimental vehicle capable of reaching orbit it has not yet been funded on april th rocky nelson of macdonnell douglas gave a talk entitled optimizing techniques for advanced space missions here at the university of illinois mr nelson s job involves using software to simulate trajectories and determine the optimal trajectory within given requirements although he is not directly involved with the delta clipper project he has spent time with them recently using his software for their applications he thus used the dc y project for most of his examples while i don t think the details of implicit trajectory simulation are of much interest to the readers i hope they aren t i fell asleep during that part i think that many of you will be interested in some of the details gleaned from the examples the first example given was the maximization of payload for a polar orbit the main restriction is that acceleration must remain below gs i assume that this is driven by passenger constraints rather than hardware constraints but i did not verify that the delta clipper y version has engines boosters and sustainers the boosters which have a lower isp are shut down in mid flight thus one critical question is when to shut them down mr nelson showed the following plot of acceleration vs time g as ascii graphs go this is actually fairly good the big difference is that the lines g made by the should be curves which are concave up the data is only approximate as the graph wasn t up for very long g g sec sec as mentioned before a critical constraint is that g levels must be kept below initially all eight engines are started as the vehicle burns fuel the accelleration increases as it gets close to g the booster engines are throtled back however they quickly become inefficient at low power so it soon makes more sense to cut them off altogether this causes the dip in accelleration at about seconds eventually the remaining sustainer engines bring the g level back up to about and then hold it there until they cut out entirely the engine cutoff does not acutally occur in orbit the trajectory is aimed for an altitude slightly higher than the nm desired and the last vestiges of air drag slow the vehicle slightly thus lowering the final altitude to that desired questions from the audience paraphrased q would it make sense to shut down the booster engines in pairs rather than all at once a very perceptive worth considering they have not yet done the simulation shutting down all four was part of the problem as given q so what was the final payload for this trajectory a can t tell us read aviation leak he also apparently had a good propulsion example but was told not to use it my question does anyone know if this security is due to sdio protecting national security or md protecting their own interests the second example was reentry simulation from orbit to just before the pitch up maneuver the biggest constraint in this one is aerodynamic heating and the parameter they were trying to maximize was crossrange he showed graphs of heating using two different models to show that both were very similar and i think we were supposed to assume that this meant they were very accurate the end result was that for a polar orbit landing at ksc the dc y would have about degrees of crossrange and would start it s reentry profile about degrees south latitude i would have asked about the landing maneuvers but he didn t know about that aspect of the flight profile josh hopkins jbh uxa cso uiuc edu find a way or make one attributed to hannibal
