Pegasus

by Jean-Jacques Serra
Orbital Science Corp. (OSC) started the design of the Air-Launched Space Booster (ASLB) alias Pegasus in April 1987. Pegasus is composed of three stages with wings, made of composit structure, powered with solif fuel and inertial guidance.

In it's standard version, Pegasus is 14.8 m long by 1.27 m diameter. It has a triangular flying surface of 6.7 m span and a rear 3-drift empennage. It weighs about 18.3 tons without the payload.

The carrier aircraft (B52 or L1011) jettisons Pegasus at 12000 m altitude at Mach 0.8. The launcher's propulsion is provided by 3 Hercules stages. The first stage is a fixed-nozzle Orion 50S, piloted by aerodynamical control surfaces. It provides 49.6 t thrust during 73 s. The second stage (same diameter) is a flexible-nozzle Orion 50 which delivers 12.5 t thurst during 72 s. The third stage is an Orion 38 with flexible nozzle that burns during 65 seconds providing 4.4 t thrust. The 2nd and 3rd stage mobile nozzles provide yawing and pitching guidance while rolling guidance is made with gas propellers which are also used for attitude control during the ballistic phases, and orientation and initial spin of the payload.

The payload mass of the standard version ranges from 270 to 410 kg depending on the orbit inclination. OSC made enhanced versions available:
- additional 4th stage (liquid fuel): HAPS (Hydrazine Auxiliary Propulsion System)
- lengthement of the 2 first stages (+24% propellant in the first stage, +30% in the second)
This version named Pegasus XL is 16.5 m long and weighs 22.7 tons. Its performance are 60% better than the original design.

Introduced in 1990 Pegasus had a difficult time obtaining a working launcher. Eight standard Pegasus were launched with success, the last one in May 1996. Nowadays only the XL version is produced. The two first launches were failures. After 3 successes the 6th model performed correctly but failed to release its payload.

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Pegasus launches

#	Launch id	Payload	Launch Date	Site	Type	Status/Comment (orbit in perigee x apogee x inclination x period)
1	90028	A: Pegsat B: Glomr 2 (USA 055)	5 Apr 1990	E, B52		480 km x 680 km x 94°
2	91051	Microsat 1 to 7	17 Jul 1991	E, B52	HAPS	Partial failure 350 km x 450 km x 82°
3	93009	A: Orbcomm XP 1 B: SCD 1	9 Feb 1993 at 14:30 UT	C, B52		730 km x 790 km x 25°
4	93026	Alexis	25 Apr 1993 at 13:56 UT	E, B52		Satellite damaged
5	94029	Step 2	19 May 1994 at 17:03 UT	E, B52	HAPS	The perigee was lower than expected 600 km x 830 km x 82°
6	n/a	Step 1	27 Jun 1994	V, L1011	XL	Failure: malfunctioned during the first stage burn, had to be destroyed
7	94046	Apex	3 Aug 1994 at 14:39 UT	V, B52		365 km x 2550 km x 70°
8	95017	A: Orbcomm FM 1 B: Orbcomm FM 2 C: Microlab 1	3 Apr 1995	V, L1011
9	n/a	Step 3	22 Jun 1995 at 19:58 UT	V, L1011	XL	Failure: interstage didn't separate from 2nd stage
10	96014	REX 2	09 Mar 1996 at 01:33 UT	V, L1011	XL
11	96031	MSTI 3	17 May 1996 at 02:44 UT	V, L1011
12	96037	TOMS	02 Jul 1996 at 07:48 UT	V, L1011	XL
13	96049	Fast	21 Aug 1996 at 09:47 UT	V, L1011	XL
14	96061	SAC B HETE	4 Nov 1996 at 17:09 UT	W	XL	the 2 payloads failed to separate from the third stage
15	97018	A: Minisat 01 B: Celestis 1	21 Apr 1997 at 11:59 UT	L1011	XL	launched from the Canary islands
16	97037	Orbview 2	1 Aug 1997 at 20:20 UT	V, L1011	XL
17	97047	Forte	29 Aug 1997 at 15:00 UT	V	XL
18	97063	Step 4	22 Oct 1997 at 13:15 UT	W	XL
19	97084	A: Orbcomm FM 5 B: Orbcomm FM 6 C: Orbcomm FM 7 D: Orbcomm FM 8 E: Orbcomm FM 9 F: Orbcomm FM 10 G: Orbcomm FM 11 H: Orbcomm FM 12	23 Dec 1997 at 19:11 UT	W	XL	HAPS fourth stage
20	98012	A: SNOE B: Teledesic 1	26 Feb 1998 at 07:07 UT	V	XL
21	98020	Trace	02 Apr 1998 at 02:42 UT	V	XL
22	98046	A: Orbcomm FM 13 B: Orbcomm FM 14 C: Orbcomm FM 15 D: Orbcomm FM 16 E: Orbcomm FM 17 F: Orbcomm FM 18 G: Orbcomm FM 19 H: Orbcomm FM 20	02 Aug 1998 at 16:24 UT	W	XL HAPS
23	98053	A: Orbcomm FM 21 B: Orbcomm FM 22 C: Orbcomm FM 23 D: Orbcomm FM 24 E: Orbcomm FM 25 F: Orbcomm FM 26 G: Orbcomm FM 27 H: Orbcomm FM 28	23 Sep 1998 at 17:06 UT	W	XL HAPS	HAPS
24	98060	SCD 2	23 Oct 1998 at 00:02 UT	C	H	this first stage carried a NASA experiment to study hypersonic boundary layer separation
25	98070	Swas	6 Dec 1998 at 00:57 UT	V	XL
26	99011	Wire	5 Mar 1999 at 02:56 UT	V	XL
27	99026	Terriers Mublcom	18 May 1999 at 05:09 UT	V	XL/H
28	99065	A: Orbcomm FM 30 B: Orbcomm FM 31 C: Orbcomm FM 32 D: Orbcomm FM 33 E: Orbcomm FM 34 F: Orbcomm FM 35 G: Orbcomm FM 36	4 Dec 1999 at 18:53 UT	W	XL	372 x 827 km x 41° only 7 satellites (usually there are 8)
29	00030	Step 5	7 Jun 2000 at 13:19 UT	V	XL	403 x 1704 km x 69°
30	00061	Hete 2	9 Oct 2000 at 05:38 UT	K		standard Pegasus with slight modifications
31	n/a	Hyper-X 1	2 Jun 2001	E	HXLV	failure: veered off course
32	02004	Hessi	5 Feb 2002 at 20:58 UT	C	XL
33	03004	Sorce	25 Jan 2003 at 20:13 UT	C	XL
34	03017	Galex	28 Apr 2003 at 11:59 UT	C	XL
35	03030	Orbview 3	26 Jun 2003 at 18:53 UT	V	XL
36	03036	Scisat 1	13 Aug 2003 at 02:09 UT	V	XL
37	05014	Dart	15 Apr 2005 at 17:26 UT	V	XL
38	06008	A: ST5 A B: ST5 B C: ST5 C	22 Mar 2006 at 14:04 UT	V	XL
39	07015	AIM	25 Apr 2007 at 20:26 UT	V	XL
40	08017	C/NOFS	16 Apr 2008 at 17:02 UT	K	XL
41	08051	Ibex	19 Oct 2008	K	XL
42	12031	NuStar	13 Jun 2012 at 16:01 UT	K	XL
43	13033	Iris US	28 Jun 2013 at 02:27 UT	V	XL
44	16078	Cygnss A to H	15 Dec 2016 at 13:37 UT	C	XL
45	19068	Icon	11 Oct 2019 at 00:31 UT	C	XL
46	21051	TacRL-2 Odyssey	13 Jun 2021 at 08:11 UT	V	XL	405 x 452 km x 97.5°

Notes: in the launch site column C stands for Cape Canaveral and released at sea, E stands for Edwards and released at Point Arguello, K stands for Kwajalein Missile Range (Marshall Islands), V stands for Vandenberg and released at Point Arguello, and W stands for Wallops. This indication is followed by the airplane type

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Future

OSC plans to equip Pegasus XL with two turbojets. Once released at 12000 m altitude the Pegasus Turbo will be accelerated by its turbojets to reach 30000 m altitude at over Mach 4. OSC claims the 30.8 t Pegasus Turbo will be 125% more powerful than Pegasus XL and could orbit 1000 kg in LEO.

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