Northrop Grumman Pegasus


Pegasus is an air-launched rocket developed by Orbital Sciences Corporation and now built and launched by Northrop Grumman Innovation Systems. Capable of carrying small payloads of up to into low Earth orbit, Pegasus first flew in 1990 and remains active. The vehicle consists of three solid propellant stages and an optional monopropellant fourth stage. Pegasus is released from its carrier aircraft at approximately, and its first stage has a wing and a tail to provide lift and attitude control while in the atmosphere. Notably, the first stage does not have a Thrust Vector Control system. Pegasus is the world's first privately developed space launch vehicle.

History

Pegasus was designed by a team led by Antonio Elias. The Pegasus's three Orion solid motors were developed by Hercules Aerospace specifically for the Pegasus launcher but using advanced carbon fiber, propellant formulation and case insulation technologies originally developed for the terminated USAF Small ICBM program. The wing and fins' structures were designed by Burt Rutan and his company, Scaled Composites, which manufactured them for Orbital.
Started in the spring of 1987, the development project was funded by Orbital Sciences Corporation and Hercules Aerospace, and did not receive any government funding. NASA did provide the use of the B-52 carrier aircraft on a cost-reimbursable basis during the development and the first few flights. Two Orbital internal projects, the Orbcomm communications constellation and the OrbView observation satellites, served as anchor customers to help justify the private funding.
DARPA purchased the first flight and options for five more, but only exercised the first of the five options. The DARPA contract was subsequently transferred to the U.S. Air Force which exercised the remaining four options. In 1993 NASA issued a Request for Proposals for a Small Expendable Launch Vehicles Services requiring a performance slightly higher than the original Pegasus, resulting in Orbital and Hercules developing the XL version to satisfy the NASA SELVS requirement.
There were no Pegasus test launches prior to the first operational launch on April 5, 1990 with NASA test pilot and former astronaut Gordon Fullerton in command of the carrier aircraft. Initially, a NASA-owned B-52 Stratofortress NB-008 served as the carrier aircraft. By 1994, Orbital had transitioned to their "Stargazer" L-1011, a converted airliner which was formerly owned by Air Canada. The name "Stargazer" is an homage to the television series : the character Jean-Luc Picard was captain of a ship named Stargazer prior to the events of the series, and his first officer William Riker once served aboard a ship named The Pegasus |Pegasus.
During its 44-launch history, the Pegasus program had three mission failures, and two partial failures, followed by 30 consecutive successful flights for a total program success rate of 89%.. The first partial failure on July 17, 1991 caused the 7 USAF microsatellites to be delivered to a lower than planned orbit, significantly reducing the mission lifetime. The last mission failure on November 4, 1996 resulted in the loss of gamma-burst identifying satellite HETE in 1996..
spacecraft.
The Pegasus XL, introduced in 1994 has lengthened stages to increase payload performance. In the Pegasus XL, the first and second stages are lengthened into the Orion 50SXL and Orion 50XL, respectively. Higher stages are unchanged; flight operations are similar. The wing is strengthened slightly to handle the higher weight. The standard Pegasus has been discontinued; the Pegasus XL is still active as of 2019. Pegasus has flown 44 missions in both configurations, launching 91 satellites as of October 12, 2019.
Dual payloads can be launched, with a canister that encloses the lower spacecraft and mounts the upper spacecraft. The upper spacecraft deploys, the canister opens, then the lower spacecraft separates from the third-stage adapter. Since the fairing is unchanged for cost and aerodynamic reasons, each of the two payloads must be relatively compact. Other multiple-satellite launches involve "self-stacking" configurations, such as the ORBCOMM spacecraft.
For their work in developing the rocket, the Pegasus team led by Antonio Elias was awarded the 1991 National Medal of Technology by U.S. President George H. W. Bush.
The initial launch price offered was US$6 million, without options or a HAPS maneuvering stage. With the enlargement to Pegasus XL and the associated improvements to the vehicle, baseline prices increased. In addition, customers usually purchase additional services, such as extra testing, design and analysis, and launch-site support.
As of 2015, the most recent Pegasus XL to be purchased—a planned June 2017 launch of NASA's Ionospheric Connection Explorer mission—had a total cost of $56.3 million, which NASA notes includes "firm-fixed launch service costs, spacecraft processing, payload integration, tracking, data and telemetry and other launch support requirements." A series of technical problems delayed this launch, which finally took place on 11 October 2019.
In July 2019, it was announced that Northrop had lost the launch contract of the IXPE satellite to SpaceX. IXPE had been planned to be launched by a Pegasus XL rocket, and had been designed so as to fit within the Pegasus XL rocket constraints. With the IXPE launch removed from the Pegasus XL rocket, there are currently no space launch missions announced for the Pegasus XL rocket. The future NASA Explorer program mission PUNCH was planned to be launched by Pegasus XL; but then NASA decided to merge the launches of PUNCH and another Explorer mission, TRACERS. These two space missions, consisting of 6 satellites in total, are to be launched by one rocket. It is expected that a larger launcher will be chosen for this dual mission launch.
Northrop has 2 Pegasus XL's remaining in its inventory. It is looking for customers for those rockets. Northrop does not plan on retiring the Pegasus XL rocket as of October 2019.
For many small satellites it is desirable to be the primary payload and be placed into the orbit desired, rather than be a secondary payload placed in a compromise orbit. For example, Pegasus launched from equatorial launch sites can put spacecraft in orbits avoiding the South Atlantic Anomaly which is desirable for many scientific spacecraft. For some payloads, this may justify the higher cost of Pegasus relative to satellites launched as secondary cargoes on larger launchers.

Launch profile

In a Pegasus launch, the carrier aircraft takes off from a runway with support and checkout facilities. Such locations have included Kennedy Space Center / Cape Canaveral Air Force Station, Florida; Vandenberg Air Force Base and Dryden Flight Research Center, California; Wallops Flight Facility, Virginia; Kwajalein Range in the Pacific Ocean, and the Canary Islands in the Atlantic. Orbital offers launches from Alcantara, Brazil, but no known customers have performed any.
Upon reaching a predetermined staging time, location, and velocity vector the aircraft releases the Pegasus. After five seconds of free-fall, the first stage ignites and the vehicle pitches up. The 45-degree delta wing aids pitch-up and provides some lift. The tail fins provide steering for first-stage flight, as the Orion 50S motor does not have a thrust-vectoring nozzle.
Approximately 1 minute and 17 seconds later, the Orion 50S motor burns out. The vehicle is at over 200,000 feet in altitude and hypersonic speed. The first stage falls away, taking the wing and tail surfaces, and the second stage ignites. The Orion 50 burns for approximately 1 minute and 18 seconds. Attitude control is by thrust vectoring the Orion 50 motor around two axes, pitch and yaw; roll control is provided by nitrogen thrusters on the third stage.
Midway through second-stage flight, the launcher has reached a near-vacuum altitude. The fairing splits and falls away, uncovering the payload and third stage. Upon burnout of the second-stage motor, the stack coasts until reaching a suitable point in its trajectory, depending on mission. Then the Orion 50 is discarded, and the third stage's Orion 38 motor ignites. It too has a thrust-vectoring nozzle, assisted by the nitrogen thrusters for roll. After approximately 64 seconds, the third stage burns out.
A fourth stage is sometimes added for a higher altitude, finer altitude accuracy, or more complex maneuvers. The HAPS is powered by three restartable, monopropellant hydrazine thrusters. As with dual launches, the HAPS cuts into the fixed volume available for payload. In at least one instance, the spacecraft was built around the HAPS.
Guidance is via a 32-bit computer and an IMU. A GPS receiver gives additional information. Due to the air launch and wing lift, the first-stage flight algorithm is custom-designed. The second- and third-stage trajectories are ballistic, and their guidance is derived from a Space Shuttle algorithm.

Carrier aircraft

The carrier aircraft serves as a booster to increase payloads at reduced cost. is only about 4% of a low earth orbital altitude, and the subsonic aircraft reaches only about 3% of orbital velocity, yet by delivering the launch vehicle to this speed and altitude, the reusable aircraft replaces a costly first-stage booster.
The single biggest cause of traditional launch delays is weather. Carriage to 40,000 feet takes the Pegasus above the troposphere, into the stratosphere. Conventional weather is limited to the troposphere, and crosswinds are much gentler at 40,000 feet. Thus the Pegasus is largely immune to weather-induced delays and their associated costs, once at altitude..
Air launching reduces range costs. No blastproof pad, blockhouse, or associated equipment are needed. This permits takeoff from a wide variety of sites, generally limited by the support and preparation requirements of the payload. The travel range of the aircraft allows launches at the equator, which increases performance and is a requirement for some mission orbits. Launching over oceans also reduces insurance costs, which are often large for a vehicle filled with volatile fuel and oxidizer.
Launch at altitude allows a larger, more efficient, yet cheaper first-stage nozzle. Its expansion ratio can be designed for low ambient air pressures, without risking flow separation and flight instability during low-altitude flight. The extra diameter of the high-altitude nozzle would be difficult to gimbal. But with reduced crosswinds, the fins can provide sufficient first-stage steering. This allows a fixed nozzle, which saves cost and weight versus a hot joint.
A single-impulse launch results in an elliptical orbit, with a high apogee and low perigee. The use of three stages, plus the coast period between second- and third-stage firings, help to circularize the orbit, ensuring the perigee clears the Earth's atmosphere. If the Pegasus launch had begun at low altitude, the coast period or thrust profile of the stages would have to be modified to prevent skimming of the atmosphere after one pass.
For launches which do not originate from Vandenberg Air Force Base, the carrier aircraft is also used to ferry the assembled launch vehicle to the launch site. For such missions, the payload can either be installed at the base and ferried by the launch vehicle or be installed at the launch site.
In October 2016, Orbital ATK announced a partnership with Stratolaunch Systems to launch Pegasus-XL rockets from the giant Scaled Composites Stratolaunch, which could launch up to three Pegasus-XL rockets on a single flight.

Related projects

Pegasus components have also been the basis of other OSC launchers. The ground-launched Taurus rocket places the Pegasus stages and a larger fairing atop a Castor 120 first stage, derived from the first stage of the MX Peacekeeper missile. Initial launches used refurbished MX first stages.
The Minotaur I, also ground-launched, is a combination of stages from Taurus launchers and Minuteman missiles, hence the name. The first two stages are from a Minuteman II; the upper stages are Orion 50XL and 38. Due to the use of surplus military rocket motors, it is only used for US Government and government-sponsored payloads.
A third vehicle is dubbed Minotaur IV despite containing no Minuteman stages. It consists of a refurbished MX with an Orion 38 added as a fourth stage.
The NASA X-43A hypersonic test vehicles were boosted by Pegasus first stages. The upper stages were replaced by exposed models of a scramjet-powered vehicle. The Orion stages boosted the X-43 to its ignition speed and altitude, and were discarded. After firing the scramjet and gathering flight data, the test vehicles also fell into the Pacific.
The most numerous derivative of Pegasus is the booster for the Ground-based Midcourse Defense interceptor, basically a vertical launched Pegasus minus wing and fins, and with the first stage modified by addition of a Thrust Vector Control system.

Launch statistics

Rocket configurations

Launch sites

Launch outcomes

Carrier airplane

Launch history

Pegasus has flown 44 missions between 1990 and 2019.

Planned launches

As of 12 October 2019 there are no space launch missions declared for the Pegasus XL rocket.

Launch failures