The Millennium Express

The chart above compares launch-cost estimates for various types of launch vehicles. On the scale depicted on the Y-axis -- millions of kg per year -- expendable launch vehicles  (ELVs) barely show.  The world currently spends more than $5 billion per year on current ELVs.  However, this only pays for launching about 350,000 kg of payload per year, or about a third of million kg per year.  The currently proposed single-stage-to-orbit (SSTO) reusable launch vehicle (RLV) would improve launch economics greatly, if the market for such a vehicle would appear overnight.  However, an SSTO may take a $6 billion investment before it could become operational.  If this were a private investment spread over a four-year period and if expected return on investment (ROI) were perhaps 26 percent per year (three-year doubling time), then revenue operations would have to produce about $1.8 billion per year.   This would be before any money is spent for recurring operational costs.  SSTO recurring operational costs might only be about $5 million per flight. And these would drop even more at higher traffic levels in accordance with a "learning curve."  However, at traffic levels of perhaps 25 flights per year, the ROI part of the price would have to be about $72 million per flight.  The main problem is that it will take time to transition from an ELV-based market measured in terms of hundreds of tonnes per year of high-cost payloads to an RLV-based market measured in terms of tens of thousands of tonnes per year of low-cost payloads.  The SSTO is not economically attractive during this transition period. Our Millennium Express two-stage-to-orbit (TSTO) RLV addresses this transition problem by minimizing pre-operational investment.  We hope to hold investment to about $170 million (2001 dollars).  We assume $200 million for purposes of the above chart.   We also expect to hold per flight recurring operational costs to about $240,000 to $300,000 per flight, since our orbiter is quite small and does not rely on any exotic technology.  In fact, the orbiter is powered by rocket engines that have been mothballed for 25 years.  Our preferred subsonic carrier stage is a modification of an aircraft that has been flying for 36 years -- powered by engines that have been flying for 46 years.  With the economics promised by the Millennium Express, we expect to make economic sense with a relatively small amount of initial revenue, i.e. as little as $100 or $200 million per year.  This enables consideration of a vertical integration strategy.  Thus, our initial business is likely to be telecommunications.  However, we also expect to be able to offer attractively prices space tourism services -- once the regulatory hurdles become manageable. Our payload is also much smaller than the payload for the SSTO, of course.  However, our recurring cost per kg of payload to low Earth orbit (LEO) promises to be only about 40 percent that for the SSTO.  The SSTO is attractive to potential customers desiring large payloads.  An SSTO is also operationally attractive.  However, we believe our approach to a TSTO/RLV also provides for relatively simple operations.  Once the transition is made to an RLV-based market, there should be room for a variety of RLVs.  We believe that our Millennium Express is the key to making the transition happen.

This rendering depicts the orbiter stage of the Millennium Express as it might look just prior to approach and landing at the original launch site.  The Millennium Express is a two-stage-to-orbit reusable launch vehicle (RLV) that stages subsonically at about mach 0.5 and a 15-km altitude and high flight path angle.  This launch approach allows us to avoid large aerodynamic forces that would otherwise design the orbiter wing.  The preferred concept for the carrier stage uses a large straight wing and large turboprop engines to allow efficient climb while constraining aerodynamic forces on the orbiter wing during the climb to launch altitude.  The carrier stage also use rocket assist above about 10-km altitude to reach 15 km and relatively thin air prior to separation of the orbiter from the carrier stage.  The orbiter stage follows an essentially ballistic trajectory after separation at a high flight path angle.  Thus the orbiter wing is used only for reentry, approach and landing.  This is the key design trick for the Millennium Express -- a design trick that we hope to patent.  The savings in orbiter wing mass is equivalent to perhaps six times the system payload.  Our performance and cost goals are dependent upon good system design and some design tricks -- not on exotic technology.  We treat our goal of constraining pre-operational investment to under $200 million as a basic design requirement. In the rendering above, the ventral fins have been translated forward from their aft reentry position.  In their forward position, these ventral fins also serve as landing skids in conjunction with a steerable nose wheel.  The X-15 used this arrangement.  The aft position of these ventrals is necessary during reentry to avoid severe heating problems associated with ventral intersections with a lower surface.  The ventrals are rotated upward for ground clearance prior to takeoff of the carrier stage -- or during landing with the orbiter stage still attached. The orbiter stage is powered by one Lyulka D-57 LOX / hydrogen and two Kuznetsov NK-39 LOX / kerosene rocket engines.  These engines are offered by GenCorp / Aerojet of Sacramento, California in accordance with a long-standing marketing agreement with Russian engine companies.  These engines were first manufactured in the mid-1970s, and have been mothballed since that time.  Nonetheless, specific impulse of the D-57 is 4472 m/s and thrust is about  370,000 newtons; specific impulse of the NK-39 engines with the fully expanded nozzle is 3452 m/s and thrust is in the 400,000 newton class.  See Astronautix.com.  Near the end of burn, we shall use only the D-57 engine to limit acceleration and to maximize specific impulse.  Aerojet plans to improve the throttling capability of all of these engines-- as they have with the similar, but larger AJ-26 engine they are providing to Kistler Aerospace for the K-1 RLV. However, our three-engine approach does not require much throttling to limit acceleration forces for missions with people on board to 3-gs. The passenger version carries sixteen passengers -- in addition to the pilot and copilot / flight attendant. Cargo payload to a 110-km, 60-degree orbit is an estimated 1800 kg. The cargo bay is suitable for a 3.6-meter long by 3-meter diameter satellite.  This is our primary orbit for our primary application:  a large number of self-propelled communications satellite for deployment to 800-km altitude. Our secondary orbit is a 450-km, 15-degree orbit for assembly of large geosynchronous satellites.  Payload to this orbit is about 2400 kg.  Cargo flights also carry a pilot and one copilot / crew member. Following is a two-view of the  passenger version of the orbiter stage.

The flight deck and cabin areas comprise the upper portion of the nose section.  The cabin floor ramps upward to make full utilization of the available space.  The aft portion of the cabin is elevated sufficiently to allow a small elevator aft and a lower deck with two toilets. The spherical helium tank forms the nose of the vehicle.  The nose gear and part of the kerosene is located below the flight deck; the remaining portion of the kerosene is below the forward portion of the cabin.  The large liquid hydrogen tank for the low density hydrogen is located just behind the cabin; the liquid oxygen (LOX) tank is aft of the hydrogen tank and forward of the engine compartment.  There is very little  shift in the center of gravity during rocket burn. Following is a two-view of the cargo version of the orbiter of the Millennium Express.

The cargo door accommodates cylindrical payloads up to 3 meters in diameter and 3.6 meters in length.  A conical shaped payload could be somewhat wider at one end.  For structural reasons, the door is a single piece, not a clamshell arrangement as on the Space Shuttle.  As with the passenger version, kerosene occupies the lower portion of the nose section that includes the payload bay.  However, the cargo deck is much lower than the deck of the passenger cabin, and the kerosene -- plus the nose gear -- occupies the entire lower portion of the nose section.  The cargo version deck is indented to accommodate a 3-meter diameter preassembled payload.  A special adaptor provides a level deck for other purposes. Whereas the passenger version is designed to reenter and land with a full payload, the cargo version is designed to reenter and land empty.  This necessitates moving the wing aft about 2 meters for proper balance.  At gross mass, the cargo version is too stable.  However, the orbiter flies a basically ballistic trajectory during exit.  Accordingly, the overly stable condition at separation should not be a problem.

Our preferred concept for the carrier stage is modification of the Antonov An-22 Antheus large turboprop transport. This aircraft was developed 36 years ago for transporting military cargo.  Aeroflot used a later version as a commercial transport.  The An-22 is powered by four Kuznetsov 15,000 HP turboprop engines and counter-rotating propellers.  In case you're wondering -- yes, you're right, that's the same Kuznetsov that built the NK-39 rocket engines that we plan to use in the orbiter. Three major modifications are necessary to make the An-22 suitable for our concept for the carrier stage of the Millennium Express.  First, we shall have to move the main gear outboard into pods suspended on pylons.  This allows us to carry a winged orbiter near the center of gravity and under the An-22.  We then want to cut a cavity in the belly of the An-22 to carry the orbiter in semi-submerged fashion.  We shall also have to beef up some of the fuselage structure that is otherwise weakend for the cutout; we shall also have to find or to develop appropriate hardpoints for suspension of the orbiter and for extending the orbiter below the An-22 fuselage prior to separation. The other major modification is to install a rocket assist system for subsonic climb from 10 km to 15 km at perhaps a 30-degree flight path angle.   Some of the NK-39 engines already come with truncated nozzles; a pair of these engines may be suitable.  At the present time, we also show the orbiter dorsal vertical protruding through a slot in the upper fuselage of the An-22 behind the wing carrythrough.  If  this proves to be impractical, then we should either make the orbital vertical somewhat stubbier, or we would fold it partly. The An-22 is very well suited for our purposes.  We want simple, straightforward operations.  We also want to be able to climb efficiently to altitude at relatively low speed to preclude having the orbiter wing encounter large aerodynamic forces.  The Kuznetsov NK-12 turboprop engine is much larger than any other turboprop engine in the world.  It is also used on the Tupolov Tu-95 "Bear" bomber and other aircraft.  The An-22 has a large straight wing that is appropriate for medium-speed climb to relatively high altitude.  The fuselage diameter is nearly half again the diameter of our proposed orbiter -- thereby permitting the semi-submerged approach.  The An-22 has a normal gross mass at takeoff of 250 tonnes. Following is a three view of the modified An-22 with the Millennium Express orbiter attached.  Not much of the orbiter shows in these views; a bottom view would show more of the orbiter.

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