A continuing series for the gravitationally impaired,
Burt Rutan's Spaceship One went to an altitude of 62 miles to earn astronaut wings for its two pilots. Great job guys!! They got to experience about five minutes of zero gravity and a 5 Gee reentry. Richard Branson wants to offer $200,000 rides for space tourists on Spaceship Two. That's a lot of money for a 5 minute ride! To get more zero Gee time you need to go into Low Earth Orbit OR . . . . . go very much higher in a suborbital trajectory. By going to a very high altitude suborbital flight you could get anywhere from up to a couple of hours of zero Gee time to a couple of days, but it's not without some very real dangers.
Staying suborbital but going very high has two advantages, less energy, and no guidance system. The big disadvantages are, exposure to the Van Allen radiation belts and a high Gee and heat load on reentry. The Van Allen belts are not a big hazard, but they are a marketing problem, nobody wants to fly through radiation even if it is a short exposure and free. By moving the launch site to a high latitude the belts can be sidestepped. THE big problem of a vertical reentry is the high gee load and the very high heat load. Orbital vehicles hit the atmosphere at a low angle and spread the gee load and the energy over a long period of time. The same effect can be had for a suborbital flight by going very high, and then adding a second impulse at apogee, enough to move the reentry point to the limb of planet Earth. This will result in a reentry profile very similar to the Apollo lunar missions. The timing of the second impulse is not critical and ample opputunity is available for astronavagation by star fix with a sextant. The big danger is, missing the second impulse entirely. This failure mode will result in a brutal vertical reentry, NOT GOOD! Also put a little too much on the second impulse and you'll slip into a highly elliptical orbit around earth with the oppurtunity to reenter (with a minor thruster burn at apogee) on a later orbit. Of course this could be what you're trying to do. Burt Rutan, Are you listening?