pogrslts.htm
Capabilities of Existing Aircraft Systems
Table 1 lists some of the velocity and altitude capabilities
of eight aircraft considered most useful for comparison purposes.
All data were extracted from various issues of Janes' All
the World's Aircraft[8],
except data on the X-7A.[d]
[d] Personal communique with Andreas Gehrs-Pahl, collector of
military missile information, 14 Jun 95
AIRCRAFT ENGINE DATE MACH ALTITUDE NOTE F-104 J-79 1950s 2.2 >90,000 Zoom{1} F-4 J-79 1950s >2.0 71,000 Combat Ceiling{2} 98,000 TTC 6 min, 12 sec{3} MIG-25 R-31 1960s 3.2 88,000 Service Ceiling{4} 98,000 TTC 3 min, 9 sec 115,000 TTC 4 min, 11 sec 123,524 Zoom F-15 F-100 1970s 2.5 98,000 TTC 3 min, 28 sec TR-1 J-95 1950s <1.0 90,000 Operational Ceiling{5} Experimental And Special Purpose Aircraft X-7A Ramjet 1950s 4.3 XB-70 J-93 1950s >3.0 SR-71 J-58 1960s >3.0 Notes: 1. A zoom maneuver is to take the aircraft to high altitude and velocity, then pull up into a climb such that altitude is maximized, often after engine flame-out. 2. The combat ceiling is the maximum altitude recommended during combat maneuvers. 3. TTC (Time To Climb) records may have been achieved with engines flamed out. 4. The service ceiling is the maximum altitude at which the aircraft can maintain a climb rate of 100 ft/min. 5. The operational ceiling is the maximum altitude at which the aircraft can maintain a climb rate of 1,000 ft/min.
Altitude. Most people are familiar with aircraft operating below 50,000 ft altitude. It was found, however, that altitudes in excess of 100,000 ft have been achievable for several decades. Two U.S. aircraft specifically designed for these conditions are the SR-71 and TR-1. The former Soviet Union's MIG-25, which was designed to intercept the XB-70, is still operating and holds the world altitude record of more than 123,000 ft in a zoom. Typically, fighter aircraft are restricted from operating above 50,000 ft because of the safety requirement for pressure or space suits. These numbers tend to bound the expected altitude capability of a winged Pogo, using off-the-shelf engines, to between 60,000 and 100,000 ft altitude while still under power.
Velocity. The maximum Mach numbers for the fighter aircraft researched ranged from 2 to 3.2 (though not neccessarily at the same time as the maximum altitude). These appeared to be the result of the aircraft design trade-offs rather than the limits of the technologies. Typical fighter aircraft must operate efficiently over a wide range of velocities and altitudes while performing high-g maneuvering. They must also carry a range of munitions, avionics, other components, and a flight crew. Many of these design trade-offs would not be applicable to a Pogo. However, considering the technological difficulties seen by the SR-71 and the MIG-25, a winged Pogo using off-the-shelf components would probably have a dash velocity bounded between Mach 2.5 and 3.5.
Pogo Lift Capability. Current engines, such as the F-100 series, have a considerable T/W ratio. Each -220P is rated as having a static sea level thrust of 27,000 lb while weighing only 3,400 lb. Table 2 is a T/W estimate of a Five-Engine Pogo carrying a Pegasus.
Thrust (five engines at sea level) 135,000 lb Engines + Cowlings & Mounts 20,000 lb Fuel (2,500 lb for each engine) 12,500 Fuselage , Avionics, etc. 20,000 Total Pogo Weight 52,500 Pogo Excess Thrust 82,500 lb Pegasus 42,000 Total System Weight 94,500 System Excess Thrust 40,500 lb Thrust/Weight (T/W) 1.43
This excess thrust could lift the Pogo and a 42,000-lb Pegasus
with a total T/W of 1.43 and an initial vertical acceleration
of 0.43 g. By comparison, the record breaking F-15 had a T/W
of about 1.2. Additional lift capability could be gained by adding
engines up to some practical limit. This author arbitrarily chose
10 to be a quasi-practical limit.
ed note: It was later learned
that the F-15 Streak Eagle had a T/W of 1.4-1.6+ during these flights.
Improved Pogo Performance. Several possible methods of improving the performance of Pogos were considered. These were discussed in the Study Methodology section under Postulated Future Generations of Pogos and, to a greater extent, in Appendix B.
Estimated Performance Benefits to Upper-Stage Vehicles
Two example upper stages used were Pegasus and Taurus because of the availability of data and their similarity to each other. A notional LOX/LH2 fueled upper stage was also used. All were assumed to be launched from a Pogo at 100,000-ft altitude and Mach 2.5.
Analysis Methodology. Three sources were used to analyze the payload increase potential for the Pegasus and three for the Taurus. These results were expected to be roughly valid for all similar multi-stage, solid propellant, upper-stage vehicles. Other types of upper-stage vehicles, such as single stage or those using liquid propellant, should benefit to slightly greater or lesser extents. The payload for the notional LOX/LH2 upper stage was assumed and the payload increase was estimated based on a comparison to the Taurus.
Pegasus. The Pegasus is a winged, multi-stage, solid-fueled vehicle, normally air-launched.
...1) The first source was a verbal discussion with Manny Landa[e],
an expert in computer models of the Pegasus in support of
launches and launch failures. Based on his experience, Landa
provided an estimate of 70 to 80% increased payload for a Pegasus.
He was unable to complete any runs with his modeling software because
of lack of funds.
[e] Personal communique with Manny Landa, Aerospace Corporation
...2) The second source was the Analysis Branch personnel who used a commercial Program to Optimize Simulated Trajectories (POST) model. This model gave an estimate of 93% increase (from a baseline of 794 to 1,535 lb) in payload for a Pegasus. Of the three estimates this one was considered to be the most accurate and verifiable. Personnel in the Analysis Branch also performed a sensitivity analysis on altitude (see Table 3 and Fig. 5) and velocity (see Table 4 and Fig. 6).
Release Velocity Maintained At M=2.5 ALT V PL INCREASED PL (ft) (ft/sec) (lb to LEO) (percent)41,500 766 794 Baseline Pegasus 50,000 2339 1104 39 60,000 2339 1378 74 80,000 2362 1510 90 100,000 2394 1535 93 (Pogo) 120,000 2475 1601 102 140,000 2560 1626 105
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Release Altitude Maintained At 100,000 ft
MACH V PL INCREASED PL (ft/sec) (lb to LEO) (percent)0.8 766 794 Baseline Pegasus 1.5 1437 1262 59 2.5 2394 1535 93 (Pogo) 3.5 3352 1852 133 4.5 4310 2257 184
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....3) The third was a "home-grown" model that calculated trajectories based on reported thrusts and weights[13] with estimates of lift, drag, thrust, and pitch angles. This model estimated the increased payload for a Pegasus at 75 to 80%.
While the first estimate was only an expert's opinion and the third model was not calibrated, the three agreed within the bounds anticipated for such a limited study. They also agreed with an intuitive estimate that launching the Pegasus from twice as high and three times as fast as from the L-1011 should significantly increase its payload.
Taurus. The Taurus can be described as a wingless Pegasus with a launch-assist solid booster added to the bottom of the stack. It is normally a ground-launched vehicle. As of this writing only one Taurus had been launched.
...1) The same POST model used for the Pegasus was used to estimate the payload increase for a Taurus. This model gave an estimate of 142% increase (from a baseline of 2,870 to 6,930 lb) in payload for a Taurus.
...2) The "home-grown" model gave an estimated increase for the Taurus of about 200%.
...3) The third source was a comparison to HQ NASA's estimate for the "Maglev" concept[14]. This concept uses a sled on a magnetic levitation track to accelerate a launch vehicle to 15,000 ft altitude and Mach 0.8, both of which are considerably less than the Pogo. NASA expects this to increase the payload of the launch vehicle nearly 80% over ground launch from sea level.
While the above sources were inconsistent in their estimate of the amount of potential payload increase for the Taurus they all showed a significant increase. The POST model estimate is probably close for most multi-stage, solid propellant launch vehicles. Other current and proposed launch vehicles might be found that would demonstrate even more improvement.
Notional LOX/LH2 Upper Stage. The notional LOX/LH2 upper stage was assumed to weigh the same as the Taurus and have an initial payload capacity of 8,000 lb. The payload increase, when launched from the Pogo, was estimated to be roughly similar in percentage to that estimated for the Taurus (142%), or 11,000 lb.
Estimated Costs
The purpose of the Pogo concept was to significantly reduce the cost of spacelift. Without a cost estimate this study would have little meaning. However, estimates of launch vehicle costs have been historically inaccurate and low. Therefore, the costs to develop two Pogo variations were estimated but caveated that they could be off by more than a factor of two. For a Pogo cost sensitivity assessment the impact on launch costs of doubled Pogo costs were also calculated.
Five-Engine Pogo - Pegasus Upper Stage. The first variation is a Five-Engine Pogo capable of launch assisting a Pegasus-size upper stage. The cost estimates are listed in Table 5. The Pogo portion of the costs are estimated according to the following assumptions.
....1) Costs are divided into fixed costs (development and acquisition (D&A)), and recurring costs (operations and support (O&S)and unreliability).
....2) The launch rate is assumed to be 20 per year.
....3) With the assumption that the Pogo program would be treated as a commercial venture, the fixed costs are divided equally among the flights for the first four years (this is considered to approximate a five-year payback with interest, but with more simple math). The estimated costs per flight are representative of the first five years. The cost/flight will dramatically drop for years 6 through 20. Inflation is considered small and therefore excluded.
....4) O&S costs are estimated at $100,000 per flight, which
is higher than those for a fighter aircraft but less than for
typical launch vehicles. For comparison, the cost of flying an
F-16 (a single engine aircraft using a similar engine) is $9,000/hr[f].
The anticipated Pogo flight time is 10 to 15 min.
[f] Presented during a tour of the F-16 Combined Test Team facility
at Edwards AFB, Oct 1995
....5) The reliability of the Pogo is estimated at 99.5%, which is higher than current launch vehicle first stages but much lower than fighter aircraft. The estimated loss because of unreliability includes half the Pogo acquisition cost (assuming the loss is halfway through its life), the upper stage, and the payload. The per flight cost associated with this loss therefore is 0.005 times the included costs. The estimated payload value is $5 M. The estimated unreliability costs for a Five-Engine Pogo are shown in Table 6.
CATEGORY DEVELOPMENT ACQUISITION Fuselage $20 M $10 M Engines 0 17.5 Flight Controls 15 10 Ground Systems 10 0.5 Subtotal $45 M $38 MTotal D&A $83 M D&A Cost/Flight (fixed) $1 M
O&S/Flt $0.1 M Unreliability 0.2 Subtotal (Recurring) $0.3 Total Pogo Cost/Flt $1.3 M
Pogo Cost/741-lb Increase (Incremental) $1,754/lb
Total Launch Cost/1,535-lb Payload (Total) (Pogo + Pegasus = $11.3 M) $7,362/lb
Pogo Acquisition Cost/2 $19 M Upper Stage 10 Payload 5 Total Cost $34 M Unreliability Factor x 0.005 Unreliability Cost/Flight $0.2 M (rounded)
....6) The payload is assumed to increase from a baseline of 794 to 1,535 lb (taken from the estimated payload increase described above), an increase of 741 lb.
....7) The engines are assumed to be F-100-PW-200s costing $3.5 M
each.[c]
[c] Personal communiques with Marvin Stibich, USAF Wright
Laboratories, Aeropropulsion and Power Directorate, Wright Patterson
AFB, OH
....8) The cost of a Pegasus is assumed to be $10 M[13]. The costs associated with the L1011 carrier aircraft are considered negligible.
Ten-Engine Pogo - Taurus Upper Stage. The second variation is a Ten-Engine Pogo capable of launch assisting a Taurus-size upper stage. The cost estimates are listed in Table 7. The Pogo portion of the costs are estimated to be similar to the Five-Engine version above with the following changes.
....1) The launch rate is assumed to be 10 per year.
....2) O&S costs per flight are estimated at $200,000 per flight.
....3) The unreliability cost is calculated with an estimated payload value of $25 M and shown in Table 8.
....4) The payload is assumed to increase from a baseline of 2,870 to 6,930 lb (the payload estimated above), an increase of 4,060 lb.
....5) The engines are assumed to be F-100-PW-229s costing $4.5 M each.[c]
CATEGORY DEVELOPMENT ACQUISITION Fuselage $20 M $20 M Engines 0 45 Flight Controls 15 15 Ground Systems 10 0.5 Subtotal $45 M $80.5 MTotal D&A $125.5 M D&A Cost/Flight (Fixed) $3.1 M
O&S/Flt $0.2 M Unreliability 0.4 Subtotal (Recurring) $0.6 Total Pogo Cost/Flight $3.7 M
Pogo Cost/4,060-lb Increase (Incremental) $911/lb
Total Launch Cost /6,930-lb Payload (Total) (Pogo + Taurus = $18.7 M) $2,698/lb
Pogo Acquisition Cost/2 $40.3 M Upper Stage 15 Payload 25 Total Cost $80.3 M Unreliability Factor x 0.005 Unreliability Cost/Flight $0.4 M (rounded)
Ten-Engine Pogo - New LOX/LH2 Upper Stage. This variation uses the same Pogo and assumptions as those used for the Ten-Engine Pogo above except for the following. The cost estimates are listed in Table 9.
CATEGORY DEVELOPMENT ACQUISITIONFuselage $20 M $20 M Engines 0 45 Flight Controls 15 15 Ground Systems 10 0.5 Subtotal $45 M $80.5 M
Total D&A $125.5 M D&A Cost/Flight (Fixed) $3.1 M
O&S/Flt $0.2 M Unreliability 0.6 Subtotal (Recurring) $0.8 Total Pogo Cost/Flight $3.9 M
Pogo Cost/11,000-lb Increase (Incremental) $355/lb
Total Launch Cost /19,000-lb Payload (Total) (Pogo + Upper Stage = $53.9 M) $2,837/lb
....1) A new LOX/LH2 expendable upper stage is used that would be optimized for the initial conditions provided by the Pogo. This upper stage could be as simple as minor modifications to an existing vehicle or as complex as a Trans Atmospheric Vehicle (TAV). The development and O&S costs associated with this upper stage are not included in this study. The acquisition cost for this upper stage is assumed to be $50 M. The estimated payload value is $25 M.
....2) Unreliability costs. The unreliability cost is calculated and shown in Table 10.
....3) The payload baseline is assumed to be 8,000 lb. With the Pogo it is estimated to be 19,000 lb, an increase of 11,000 lb. This is the same percentage increase as for the Taurus.
Pogo Acquisition Cost/2 $40.3 M Upper Stage 50 Payload Cost 25 Total Cost $115.3 M Unreliability Factor x 0.005 Unreliability Cost/Flt $0.6 M (rounded)
Cost Comparison and Sensitivity
For the above configurations the Pogo cost per flight, with amortization and unreliability costs included, ranges from 1.3 to $3.9 M (see Table 11 and Figs. 7 and 8). This translates into incremental costs for the increased payloads on the Pegasus and Taurus of $1,754 and $911/lb to LEO. Those costs are 14 and 17% of baseline costs, respectively. When the Pogo costs and upper-stage costs are combined, the total payload costs per pound are $7,362 and $2,698/lb. Those costs are 58 and 52% of the baseline launch costs.
UPPER STAGE PEGASUS TAURUS NEW LOX/LH2BASELINE COST Current Cost ($) 10M 15M 50M Current Payload (lb) 794 2,870 8,000 $/lb to LEO 12,594 5,226 6,250 Percent of Baseline (%) 100 100 100 INCREMENTAL COST Pogo Cost/flt ($) 1.3M 3.7M 3.9M Increased Payload (lb) 741 4,060 11,000 $/lb to LEO 1,754 911 355 Percent of Baseline (%) 14 17 7 TOTAL LAUNCH COST System Cost/flt ($) 11.3M 18.7M 53.9M Total Payload (lb) 1,535 6,930 19,000 $/lb to LEO 7,362 2,698 2,837 Percent of Baseline (%) 58 52 45
COST SENSITIVITY - WITH POGO COSTS X 2
INCREMENTAL COST Pogo Cost/flt ($) 2.6M 7.4M 7.8M Increased Payload (lb) 741 4,060 11,000 $/lb to LEO 3,509 1,823 709 Percent of Baseline (%) 28 35 11 TOTAL LAUNCH COST System Cost/flt ($) 12.6M 22.4M 57.8M Total Payload (lb) 1,535 6,930 19,000 $/lb to LEO 8,208 3,232 3,042 Percent of Baseline (%) 65 62 49
Notes: Incremental Cost = (Pogo Cost/flt)/(Increased Payload) System Cost = Pogo + Upper Stage Launch Cost = (System Cost/flt)/(Total Payload) Pogo Costs X 2 = Twice Originally Estimated Pogo Costs Baseline LOX/LH2 Cost = $6,250 Estimated From Current Launch Vehicles
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For the New LOX/LH2 upper stage a baseline cost of $6,250/lb to LEO is used (based on approximate current costs). This gives an incremental cost for the increased payload of $355/lb or 7% of the baseline. The total launch cost is $2,837/lb or 45% of baseline.
Because of the historical underestimating of space program costs the above numbers were recalculated for a Pogo cost sensitivity by assuming twice the estimated Pogo costs. These figures show that, as expected, the incremental costs double but still remain significantly lower than the baseline. The total launch costs increase slightly but are still well below those of the baseline.
As an aside, the incremental Pogo costs for the Taurus version, after the five-year payback period, are $148/lb. For the new LOX/LH2 upper-stage version the incremental Pogo costs are $72/lb. Total launch costs are not significantly reduced.
Concerns Identified
A number of concerns were identified throughout the period of this study and are listed below. Where possible an attempt has been made to address each.
a. Turbulent airflow at the engine inlets, because of airflow around the fuselage, could cause loss of engine performance.
This might be mitigated by placement of the engines and the wing such that the turbulence will not impinge on the engine inlets. Another possibility might be to embed the engines within the Pogo fuselage using an annular inlet and plenum (see Fig. 3) such that only laminar airflow reaches the engines. It might also be that such turbulence can be avoided. With a sufficient T/W ratio it might be possible to gain enough velocity in the vertical direction that the transition to lifting flight can be done with a very small angle of attack, thereby keeping the upper-stage turbulence small and close to the fuselage.
b. The time and expense of developing supersonic nozzles that could achieve Mach 2.5 are understated.
While the F-15 was rated at Mach 2.5 it has been stated[c] that this is not an easily achievable condition. On the other hand, the F-15 inlets are designed to operate over a wide range of speeds, altitudes, and angles of attack so that the aircraft can perform its "Air Superiority" mission. Further, Mach 2.5 is at the very edge of the F-15 flight envelope rather than its primary design speed. The Pogo is expected to a) have a much higher T/W than the F-15, b) be optimized for the higher speed, and c) be allowed greater leeway in terms of its flight profile than the F-15. While a Mach 2.5 inlet is not considered a trivial engineering task it is expected to be relatively straightforward using currently available engineering tools.
...(Editors note: Since the writing of the report there have been many concerns expressed about the performance and estimated costs of developing and building of the Pogos. An independent review by a professional aerospace consultant provided more specific concerns on both performance and costs. Because of the expertise of this individual and the depth of the review I take those comments very seriously. In response I offer the following.
The consultant felt that "the three operational prototypes might require about a $250M preoperational investment." "However, the ten-engine Pogo might save perhaps $4M per flight in operational and hardware costs relative to the expendable solid booster. Thus, these assumptions lead to a crossover point as low as about 13 flights per year."
This Page Last Updated 29 May 97