Windjammer Assisted SSTO

Depicted below is MMI's 1971 concept for an assisted single-stage-to-orbit space transport that attracted the interest of the U.S. Air Force Space and Missile Systems Organization (SAMSO). The Air Force asked the Boeing company study the concept for feasibility. Results were favorable. MMI' s Windjammer became the direct precursor of the Boeing RASV (reusable aerospace vehicle). The RASV remains to this day a viable contender for the SSTO competiition. The RASV calls for a ground sled to avoid designing the landing gear for full gross mass. The Windjammer was to use either a ground sled or a flying sled. (Note: from 1967 to 1985, MMI was known as TranSpace, and TranSpace, Inc.).

Windjammer Assisted SSTO

Click here for full-size rendering (303k bytes, 1455 x 1116 pixels). Rendering by the Boeing Company.

The Windjammer incorporates a number of design features that are necessary to make a winged SSTO -- or near-SSTO -- practical. These design features include: a) tradeoff of engine mass for wing mass by designing the horizontal takeoff and landing (HTOL) vehicle with an initial thrust-to-weight ratio perhaps one-half that for a comparatble VTOL or VTHL vehicle; b) careful placement of the dense liquid oxygen -- perhaps 76 percent of the gross mass -- so that the gross mass is closely matched with aerodynamic lift; c) carefully integration of the overall vehicle design and thermal protection system so that low planform loading results in much lower reentry heating. Point (a) has an important impact on aerodynamic stability and control, since even rocket engines can create an aft-center-of gravity balance problem for an RLV. This also decreases engine costs -- a major contributor to overall acquisition and operating costs. Point (b) has a large impact on achievable mass fraction. MMI believes that a properly designed wing-body configuration not only has better flying and landing characteristics, but can also achieve a better mass fraction than a lifting body configuration like the X-33. Point (c) is part of MMI's thermal protection system patent (U.S. patent 4,919,366).
With careful design, HTOL, VTOL, and VTHL are roughly equivalent with respect to size versus performance. However, they are not equivalent with respect to operations. The HTOL vehicle keeps ground operations closer to the ground. Moreover, HTOL vehicles generally have more cross-range, lower reentry heating, and lower landing speeds than VTHL vehicles -- and much higher cross-range and lower reentry g's than VTOL vehicles.
Our two-stage-to-orbit (TSTO) X Van is much smaller than an SSTO must necessarily be with current technology. Vertical takeoff in the vertical attitude does not greatly complicate ground operations for a small RLV. In fact, the X Van is small enough to allow rotation from the horizontal to the vertical attitude for liftoff. We are curently working on both a VTHL and HTOL version. Our HTOL flyback booster version will likely cost about $30,000,000 more to bring three operational prototypes to operational status -- relative to the VTHL, strap-on, twin booster approach. However, we currently favor the flyback booster version, because of the interest of several space tourism groups.
Since the mid-1970s, MMI has favored reusable launch vehicles (RLVs) that are much smaller than the Windjammer in order to minimize the pre-operational investment. MMI believes that -- in the near-term -- minimizing the pre-operational investment is of overriding importance for a successuful commercial approach to low-cost space transportation. Nonetheless, MMI believes that some of the tricks the company has learned over the years may make a true SSTO RLV (no sled) possible at a gross mass of about 1000 tonnes. Moreover, with tight commercial management, MMI believes that three sets of SSTO operational prototypes might be made operational within a pre-operational budget of about $1 billion. This would require, however, an upfront commercial investment commitment larger than MMI currently believes is likely.

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Depicted below is MMI's 1971 concept for an assisted single-stage-to-orbit space transport that attracted the interest of the U.S. Air Force Space and Missile Systems Organization (SAMSO). The Air Force asked the Boeing company study the concept for feasibility. Results were favorable. MMI' s Windjammer became the direct precursor of the Boeing RASV (reusable aerospace vehicle). The RASV remains to this day a viable contender for the SSTO competiition. The RASV calls for a ground sled to avoid designing the landing gear for full gross mass. The Windjammer was to use either a ground sled or a flying sled. (Note: from 1967 to 1985, MMI was known as TranSpace, and TranSpace, Inc.).

Click here for full-size rendering (303k bytes, 1455 x 1116 pixels). Rendering by the Boeing Company.
The Windjammer incorporates a number of design features that are necessary to make a winged SSTO -- or near-SSTO -- practical. These design features include: a) tradeoff of engine mass for wing mass by designing the horizontal takeoff and landing (HTOL) vehicle with an initial thrust-to-weight ratio perhaps one-half that for a comparatble VTOL or VTHL vehicle; b) careful placement of the dense liquid oxygen -- perhaps 76 percent of the gross mass -- so that the gross mass is closely matched with aerodynamic lift; c) carefully integration of the overall vehicle design and thermal protection system so that low planform loading results in much lower reentry heating. Point (a) has an important impact on aerodynamic stability and control, since even rocket engines can create an aft-center-of gravity balance problem for an RLV. This also decreases engine costs -- a major contributor to overall acquisition and operating costs. Point (b) has a large impact on achievable mass fraction. MMI believes that a properly designed wing-body configuration not only has better flying and landing characteristics, but can also achieve a better mass fraction than a lifting body configuration like the X-33. Point (c) is part of MMI's thermal protection system patent (U.S. patent 4,919,366). With careful design, HTOL, VTOL, and VTHL are roughly equivalent with respect to size versus performance. However, they are not equivalent with respect to operations. The HTOL vehicle keeps ground operations closer to the ground. Moreover, HTOL vehicles generally have more cross-range, lower reentry heating, and lower landing speeds than VTHL vehicles -- and much higher cross-range and lower reentry g's than VTOL vehicles. Our two-stage-to-orbit (TSTO) X Van is much smaller than an SSTO must necessarily be with current technology. Vertical takeoff in the vertical attitude does not greatly complicate ground operations for a small RLV. In fact, the X Van is small enough to allow rotation from the horizontal to the vertical attitude for liftoff. We are curently working on both a VTHL and HTOL version. Our HTOL flyback booster version will likely cost about $30,000,000 more to bring three operational prototypes to operational status -- relative to the VTHL, strap-on, twin booster approach. However, we currently favor the flyback booster version, because of the interest of several space tourism groups. Since the mid-1970s, MMI has favored reusable launch vehicles (RLVs) that are much smaller than the Windjammer in order to minimize the pre-operational investment. MMI believes that -- in the near-term -- minimizing the pre-operational investment is of overriding importance for a successuful commercial approach to low-cost space transportation. Nonetheless, MMI believes that some of the tricks the company has learned over the years may make a true SSTO RLV (no sled) possible at a gross mass of about 1000 tonnes. Moreover, with tight commercial management, MMI believes that three sets of SSTO operational prototypes might be made operational within a pre-operational budget of about $1 billion. This would require, however, an upfront commercial investment commitment larger than MMI currently believes is likely.