I. Opportunity Description

The use of Earth orbiting satellites is increasing rapidly, and several experts predict a nearly ten-fold increase in the number of satellites used for commerical purposes in the next few years. Great opportunities exist for companies that can provide low-cost systems that are able to place satellites into orbit. To fly in space, a rocket must overcome gravity; launching the rocket from an airplane flying at a significant altitude can reduce the amount of thrust needed, and therefore the lower the overall weight of the rocket.

Additionally, many newly developed tasks and missions can be carried out using constellations, or groups, of many small satellites in Low-Earth Orbit (LEO). Examples of satellite constellations include the Iridium constellation (which uses 66 operating satellites) and the Teledesic constellation (which uses 288 satellites) that are to provide global communications. An emerging trend is to use a large number of small satellites in LEO to provide communication, observation and scientific study.

The low-cost launch system to be designed for this proposal will consist of both a reusable aircraft capable of carrying the rocket to the necessary drop altitude and the rocket itself, capable of inserting small satellites into a low-Earth orbit. The rocket can be used to launch one satellite at a time, or several satellites in one launch. While systems like Orbital Sciences' L-1011/Pegasus have demonstrated this is feasible, the opportunity exists to provide a new aircraft and rocket system with both vehicles designed specifically for this task. This team design project will be conducted as if your team is a conceptual design group for an aerospace company, and your task is to devise the lowest-cost aircraft/rocket system that can place small satellites into low Earth orbit. Your design should then be compared to current launch systems. The senior management of your company will use your proposal to determine if a brand new aircraft/rocket system is a worthwhile endeavor.

II. Project Objectives

The objective is to design an aircraft / rocket system capable of placing 88 pound (40 kg) satellites into a high inclination low-Earth orbit. The design requires consideration of fuel efficiency and economy of the carrier aircraft with the ability to carry the rocket to a satisfactory drop site at an appropriate altitude. Within the constraints of carrier aircraft and rocket, aircraft configuration trades remain in wing design, placement and sizing, number and placement of engines; rocket configuration trades remain in drop altitude, drop velocity, parking orbit altitude, and number of satellites carried per launch. A minimum direct operating cost will be considered most desirable. Cost estimates should be made for a total of 50 satellites placed into orbit per year.

III. Requirements and Constraints

The aircraft should be airworthy and meet all applicable FAA regulations. All fuel shall be carried internally. In the event of unfavorable launch conditions, the aircraft must be able to land with the rocket attached. To ensure safety of the launch, the rocket will be dropped over the ocean, and there must be at least 180 nautical miles of ocean distance from the rocket drop and launch site to the nearest land. Takeoff and landing should be accomplished with a balanced field length of 10,000 feet or less.

Assume the satellite payload weighs 88 lb (40 kg mass), and is a cylindrical shape with 2 ft (0.6 m) diameter and 2 ft (0.6 m) length. Assume the aircraft crew (flight crew and rocket launch crew) number two (2) total, each with gear weighs 225 lb. To estimate the size of the rocket, three stages will be assumed; details of this are provided in the "Rocket Design Mission Profile" section below.

All atmospheric performance requirements are standard day.

1. Aircraft Design Mission Profile (2-crew, full fuel)


A. Warm-up, taxi and takeoff from a runway at sea level.

B. Climb to 32,000 ft.

C. Cruise at constant velocity, constant altitude to the rocket drop site. Use the best range speed at the start of the cruise as the constant velocity.

D. Climb to drop altitude.

E. Perform the drop manuever and release rocket. (As examples, the drop manuever may be a high-speed, constant-altitude dash, or could be a parabolic "pop-up" manuever to maximum altitude.)

G. Descend back to 32,000 ft.

H. Cruise back to base at constant velocity, constant altitude. Again, use best range speed at the start of the cruise.

I. Loiter for 30 minutes to allow for fuel reserves.

J. Descend to sea-level and land on runway at sea-level.

2. Rocket Design Mission Profile


A. At drop, assume rocket velocity equals drop velocity. The inclination of the launch matches the drop site latitude.

B. Assume that two stages are used to provide the boost to orbit. Model this boost as though it were following an elliptical Hohmann transfer orbit from the drop to the final orbit. Assume an impulsive burn to determine the "ideal"  needed DV for the boost.  To calculate the mass of the first stage, assume that this stage provides (DV_ideal / 2) * 1.05; the extra 5% will help model the effects of drag and gravity loss.  The structural mass of each stage should be assumed as 10% of the initial mass of each stage.  After burn-out of the first stage, the empty structural mass can be dropped.

C. Calculate the mass of the second stage, assuming that this stage provides (DV_ideal / 2).  Again, the empty structural mass of stage 2 can be dropped after burn-out.

D. After reaching orbit altitude, initiate an impulsive burn with the third stage to place the satellite in its final circular orbit, 600 km altitude,
inclination = 70º.

IV. Data Requirements

The final proposal based on the previously stated objectives, requirements, and constraints, should include the following:
1. Justify the final design. Describe why the particular aircraft/rocket configuration was selected. Present the results of design trade-offs, criteria used for selection, and list advantages as compared to other discarded alternatives. (Show and discuss evaluation matrices.) Show carpet plots used to optimize the final selected design (e.g., system gross weight as a function of drop speed and altitude, rocket weight as a function of parking orbit altitude).
2. Include a 3-view general arrangement drawing for the carrier aircraft and rocket. This drawing should be labeled with major design dimensions. (for example, fuselage or aircraft length, wing span, etc.)
3. Include an inboard profile showing placement of cockpit, fuel and equipment in the aircraft. Also include a profile for the rocket, showing placement of payload, fuel, and stages.
4. Include an illustrated description of the primary load bearing airframe structure and discuss rationale for material selection for both vehicles.
5. Summarize method used to size tail surfaces of carrier aircraft. Discuss stability and flying qualities, especially during drop of the rocket. Comment about the type of control system required.
6. Discuss method used to compute total drag of the aircraft and the rocket during atmospheric flight. Present a drag-breakdown for the aircraft and rocket.
7. Discuss method used to predict gross weight. Present a weight-breakdown for the aircraft and rocket.

V. Engine Data

Simple engine models will be made available for a high-bypass ratio turbofan (bypass ratio = 8.0) and a low-bypass ratio turbofan (bypass ratio = 1.0).

The solid rocket motors for the booster stages to be used in the design have a specific impulse of 290 sec. The "bulk density" of the fuel (including open volume in the combustion chamber) is 0.057 lb/in³. To allow for the proper nozzle size, use the ratios: and; the following diagram should provide guidance.



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Last modified April 8, 1999
crossley@ecn.purdue.edu