One addition to Bill's observations here: Range costs at the traditional ground launch ranges don't scale noticeably with launcher size, and can make air launch costs competitive with ground launch at the small end of the payload range.
A half-million in range costs is 1% of a $50m F9 launch, but if your target price per launch is $5m it's 10%, and at $1m it's 50%. Given that the aircraft also cost (somewhat) less down at the small end of the range (and also that the pull-up capability Bill mentions gets somewhat easier to obtain) there may be an economic case to be made for air-launch for smallsat launchers.
Henry On 2/16/2015 3:18 AM, Bill Claybaugh wrote:
Liam: I do not know of any reference but here are some general observations: - in general, air launch is more expensive than ground launch (I know Burt says the opposite, but he is provably wrong). - if custom built; air launch drop aircraft are typically more costly than a ground launch pad for the same size solid rocket. - annual O&M costs to maintain flight certification are typically higher than the same costs for a solid rocket ground launch pad. - horizontal drop requires a pull-up maneuver; the lowest mass way to do that is wings, but all that mass is unneeded for ground launch. The alternative is to have the drop aircraft pitch up; that requires a much higher performance aircraft. - air launch rockets want to be solids, particularly if horizontally launched. Feed system complexity and slosh issues during the pull-up add still more mass to a liquid solution which is not offset by the increased Isp. - most of the additional performance from air launch is in the higher area ratio of the first stage motor; the velocity imparted by the aircraft is trivial in comparison. - to make air launch economically competitive the aircraft has to have some other user (e.g. sub-orbital joyrides; carrying large or bulky cargo); otherwise the O&M cost quickly drives the project to the high cost, low flight rate corner of the box (Pegasus, for example). - the advantages of "any orbit; any time" are largely national security related; in the absence of such a sponsor / customer there is very little commercial justification for the higher cost of air launch. Cheaper to wait for the desired orbit to pass over the launch pad. (Which, BTW, argues for a single, all azimuth, ground launch pad.) Bill Sent from my iPhone On Feb 14, 2015, at 12:38 AM, Liam McQuellin <lmcquellin@xxxxxxxxxxx> wrote:Hi All, I am writing a paper and I am looking for a text book that describes air launch concepts. Does anyone know of any they could recommend? Thanks, Liam McQuellin Australian Space Research Institute