The photo below is from a recent Space.com article which describes a DARPA project that I believe has considerable merit. It shows an F-15 Eagle launching a high-altitude X43-based hypersonic missile. The F-15 is capable of carrying up to 11,000 kg of external payload to approximately 19,812 meters altitude, and perhaps higher (but it would be classified if it could). It is suggested that the same type of configuration could be used to launch orbital payloads.

Coincidentally the Russians have already been there, done that. According to Janes.com the Russian MiG-31D Air Superiority Fighter is a dedicated anti-satellite launch platform that was produced and flight-tested in 1986, and carried Vympel ASAT missiles. It has an external payload capacity of 5000 kg, and service ceiling of 20,600 meters.

The MiG-31S was designed to be a commercial small satellite launch variant, with a Fakel OKB Micron missile capable of delivering 100 kg payload to a 200 km orbit or a 70 kg payload into a 500 km orbit. The MiG-31S could also launch the Aerospace Rally System rocket-powered suborbital glider, for astronaut training, upper atmospheric research or space tourism.

There are a number of Russian aircraft that seem to be designed to break records, a few other MiGs and a few Sukhoi fighters for example have high payloads, high service altitudes, and long ranges. The F-15 Eagle does seem to beat them in terms of performance, even though it wasn't designed to carry the same variety of payloads.

The reason I like these aircraft is that they may be ideally suited to rendezvous with an Orbital Skyhook (ARMXER). These aircraft carry respectable multi-tonne payloads at double the altitude of Boeing 747 and other freighter aircraft. In addition they can fly vertical, upside-down, high-gee inverted dives, and chase the dog with spectacular maneuverability. Also, if they happen to be in the neighborhood of a Skyhook rendezvous opportunity, they can light the afterburners and "be there in 30 seconds".