- Fewer than 25 suborbital spaceflights have ever been conducted
- Most suborbital launches were conducted with vehicles retired decades ago
- No suborbital flight has ever carried a paying passenger
- There is no agreement on what even constitutes a suborbital spaceflight
by Douglas Messier
When Richard Branson and three Virgin Galactic employees strap into their seats aboard SpaceShipTwo VSS Unity on Sunday, they will briefly go where not very many have gone before: suborbital space.
Of the 374 attempts to launch astronauts to space since Yuri Gagarin flew into Earth orbit 60 years ago, only 23 were suborbital flights. The majority of those launches were conducted during the 1960’s using vehicles that long ago became museum pieces. One ended with the loss of the spacecraft and its pilot. And two flights were unintentional ones involving vehicles being launched into Earth orbit.
Of the nearly 600 individuals who have been to space, only 20 pilots and one crew member have made suborbital flights. Virgin Galactic’s chief astronaut trainer, Beth Moses, is the only person who was able to float around to enjoy the several minutes of weightlessness that a suborbital spaceflight provides. (She was testing out elements of the passenger cabin for future flights.) All the pilots were strapped securely in their seats flying their vehicles.
Branson and Jeff Bezos — whose suborbital flight aboard Blue Origin’s New Shepard is scheduled for July 20 — won’t be the first billionaires to fly into space. That happened three times during the 2000’s when billionaires flew to the International Space Station aboard Russian Soyuz spacecraft.
However, they will be the first billionaires to fly in suborbital vehicles that their own companies built. And they will be aboard the first spacecraft intended to carry paying passengers and scientific researchers on suborbital flights.
Both billionaires will be participating in flight tests. Virgin Galactic has flown SpaceShipTwo above 50 miles three times. Blue Origin has successfully launched New Shepard 15 times, but never with anyone on board. Bezos and three others will be the first to fly aboard the vehicle.
Defining Suborbital Spaceflight
There are two different definitions of where space begins. The U.S. government has awarded astronaut wings to crew members who have flown above 50 miles (80.5 km). The Federation Aeronautique Internationale (FAI) — an organization that keeps aviation and space records — recognizes 100 km (62.1 miles) as the boundary of space. The table below uses both definitions.
Piloted Suborbital Spaceflights, 1961-2021
|Vehicle||Type||Status||Years of Suborbital Flights||Flights Between 80.5 and 100 km (U.S. Recognized Spaceflight)||Flights Above 100+ km (FAI Recognized Spaceflight)||Number of Pilots & Crew|
|X-15 (Retired)||Air launched rocket plane||Retired||1962-68||11||2||8|
|Mercury Redstone (MR-4, MR-5)||Ballistic missile launched capsule||Retired||1961||0||2||2|
|SpaceShipOne||Air launched rocket plane||Retired||2004||0||3||2|
|SpaceShipTwo||Air launched rocket plane||Active||2018 – present||3||0||5+|
|Soyuz*||Ballistic missile launched orbital capsule||Active orbital spacecraft not intended for suborbital flights||1975, 2018||1||1||4|
* Includes four pilots and one crew member
Does not include 15 uncrewed New Shepard flight tests
There have been 23 crewed suborbital flights that have carried 20 pilots and one crew member. Fifteen of the flights flew above the U.S. government’s 50-mile (80.5 km) definition of where space begins, while eight exceeded the FAI’s 100 km (62.1 mile) limit. Two of the 23 flights were orbital launches of Soyuz spacecraft that suffered high-altitude aborts due to booster anomalies.
Let’s take a look at the suborbital flights by Virgin Galactic and Blue Origin. We will then examine the 60-year history of crewed flights to this region of space.
The SpaceShipTwo program’s powered flight test history is divided into two periods: before and after the accident. VSS Enterprise flew three successful flight before it was destroyed on its fourth powered flight on Oct. 31, 2014. The spacecraft only reached 72,000 ft (21.9 km/13.6 miles) due to limitations caused by hybrid engines that produced serious vibrations in the vehicle. That altitude was achieved after the vehicle was dropped from about 50,000 ft (15.2 km/9.5 miles).
VSS Enterprise was destroyed when the feather system designed to reconfigure the ship for reentry into the Earth’s atmosphere accidentally deployed during powered ascent. Co-pilot Mike Alsbury died in the accident; pilot Pete Siebold parachuted to safety with serious injuries.
SpaceShipTwo VSS Unity & VSS Enterprise Powered Flight Attempts, 2013-21
|Powered Flight Attempts Between 50-62.1 miles (80.5-100 km) by VSS Unity — U.S. Recognized Spaceflight||3||0||1||4|
|Powered Flight Attempts Below 50 miles (80.5 km) by VSS Unity||3||0||0||3|
|Powered Flight Attempts Below 50 miles (80.5 km) — VSS Enterprise (maximum altitude: 72,000 ft/21.9 km)||3||1||0||4|
The second SpaceShipTwo, VSS Unity, has flown six powered flights, including three above 50 miles (80.5 km) that the U.S. government recognizes as spaceflights. The vehicle also suffered an abort during an attempted spaceflight in December 2020 when a computer rebooted just as the engine was preparing to fire. The crew glided the ship to a safe runway landing.
SpaceShipTwo VSS Unity Flights Above 50 Miles, 2018-21
(Recognized as Spaceflights by U.S. Government)
|Date||Crew||Mach||Maximum Velocity||Maximum Altitude||Notes|
|December 13, 2018||Mark Stucky – C.J. Sturckow||2.9||2,295 mph (3,693 km/h)||271,330 ft (51.4 miles/82.7 km)||First suborbital flight by SpaceShipTwo|
|February 22, 2019||David Mackay — Michael Masucci — Beth Moses||3.04||2,333 mph (3,755 km/h)||295,007 ft (55.9 miles/89.9 km)||First suborbital flight with third crew member (Moses) to evaluate passenger experience; vehicle suffered serious damage to horizontal stabilizer that kept it grounded for 14 months; last powered flight from Mojave Air and Space Port|
|May 22, 2021||C.J. Sturckow — David Mackay||3.0||2,302 mph (3,704 km/h)||292,776 ft (55.45 miles/89.2 km)||Carried NASA-sponsored microgravity experiments; first spaceflight from Spaceport America in New Mexico|
If successful, Branson’s flight will be the fourth time VSS Unity will travel above 50 miles and the 10th powered flight of the eight-year old test program.
Neither VSS Enterprise nor VSS Unity has flown above 100 km (62.1 mile). That has led rival Blue Origin to say Virgin Galactic has not yet flown to space.
Blue Origin New Shepard Flights
Bezos and three companions will be aboard the 16th launch of the full New Shepard rocket and capsule system. The company also conducted a successful ground abort test that involved only the crew capsule and its escape system.
New Suborbital Spaceflights
|Flight Type||Successes||Failures||Partial Failures||Total|
|Capsule Flights Above 62.1 miles (100 km) — FAI Recognized spaceflight||12||0||0||12|
|Capsule Flights Between 50-62.1 miles (80.5-100 km) — U.S. Recognized Spaceflight||1||0||1||2|
|Planned In-flight Abort Tests||1||0||0||1|
|Ground Abort Tests (Capsule Only)||1||0||0||1|
During 14 flight tests, both the rocket and capsule landed separately back at Blue Origin’s test facility in West Texas. The lone failure occurred on the first launch when the rocket crashed during descent after separating from the crew capsule. The capsule landed safety under parachutes.
The capsule used for the in-flight abort test reached 7.1 km (4.4 miles). The rocket, which was expected to explode, survived the abort and flew to an altitude of 93.7 km (58.2 miles) before landing safely back on Earth.
Now that we’ve looked at the two on-going programs, let’s take a trip back 60 years to where crewed suborbital spaceflight began.
The United States got human piloted suborbital spaceflight off and running when a NASA Redstone booster sent Alan Shepard 187.5 km (116.5 miles) up into space aboard the Freedom 7 Mercury capsule on May 5, 1961.
Virgil I. “Gus” Grissom followed with a suborbital flight aboard Liberty Bell 7 in July. Grissom’s flight, which reached190.3 km (118.3 miles), remains the highest altitude achieved by a planned suborbital mission. (An aborted Soyuz orbital spacecraft went higher; we will discuss that flight later.)
Crewed Suborbital Mercury Flights
(Recognized as Spaceflights by FAI)
|Date||Crew||Vehicle||Mach||Maximum Velocity||Maximum Altitude||Notes|
|May 5, 1961||Alan Shepard||Mercury-Redstone 4||6.69||5,134 mph (8,262 km/h)||615,120 ft (116.5 miles/187.5 km)||First U.S. paceflight|
|July 21, 1961||Virgil “Gus” Grissom||Mercury-Redstone 5||6.74||5,168 mph (8,317 km/h)||624,400 ft (118.3 miles/190.3 km)||Second U.S. spaceflight; Highest and fastest planned piloted flight above 100 km|
The Mercury-Redstone flights were similar to the ones flown by Blue Origin’s New Shepard. Both systems involve single-stage rockets launched vertically from a pad with capsules that land under parachute. The main difference is that while the Mercury and Redstone vehicles were expendable, the New Shepard rocket and capsule are fully reusable.
The suborbital phase of the Mercury program ended with Grissom’s flight. The more powerful Atlas booster launched John Glenn into orbit on Feb. 20, 1962. Three more orbital flights were conducted before the Mercury program ended in 1963.
Mercury’s mix of flights illustrates an important point that is sometimes overlooked: a suborbital spaceflight takes only about three percent of the energy required to put a payload into low Earth orbit. A crewed spaceship returning from a suborbital flight also requires far less protection from the heat of reentry.
Eight military and NASA pilots conducted 13 suborbital flights between 1962 and 1968 using the X-15, an air-launched rocket plane that was used to research high-speed and high-altitude flight. The suborbital flights made up a small part of the X-15 program’s 199 total flights.
The three X-15 rocket planes were dropped from under the wing of a modified B-52 bomber, much in the same way that Virgin Galactic’s SpaceShipTwo is launched by its WhiteKnightTwo mother ship.
Suborbital X-15 Flights Above 50 Miles
|Date||Crew||Mach||Maximum Velocity||Maximum Altitude||Notes|
|August 22, 1963||Joseph Walker||5.58||3,794 mph (6,106 km/h)||354,200 ft (67.1 miles/108 km)||Highest X-15 flight; FAI recognized spaceflight; remained the altitude record for winged suborbital vehicles for 41 years|
|July 19, 1963||Joseph Walker||5.5||3,710 mph (5,971 km/h)||347,800 ft (65.9/106 km)||First X-15 flight above 100 km; FAI recognized spaceflight|
|July 17, 1962||Robert White||5.45||3,832 mph (6,157 km/h)||314,750 ft (59.6 miles/95.9 km)||First U.S. recognized spaceflight by winged vehicle|
|November 1, 1966||William Dana||5.46||3,750 mph (6,035 km/h)||306,900 ft (58.1 miles/93.5 km)||U.S. recognized spaceflight|
|September 28, 1965||John McKay||5.33||3,732 mph (6,006 km/h)||295,600 ft (56 miles/90.1 km)||U.S. recognized spaceflight|
|June 27, 1963||Robert Rushworth||4.89||3,425 mph (5,512 km/h)||285,000 ft (54 miles/86.9 km)||U.S. recognized spaceflight|
|June 29, 1965||Joseph Engle||4.94||3,432 mph (5,523 km/h)||280,600 ft (53.1 miles/85.5 km)||U.S. recognized spaceflight|
|October 17, 1967||William “Pete” Knight||5.53||3,856 mph (6,206 km/h)||280,500 ft (53.1 miles/85.5 km)||U.S. recognized spaceflight|
|January 17, 1963||Joseph Walker||5.47||3,677 mph (5,918 km/h)||271,700 ft (51.5 miles/82.81 km)||U.S. recognized spaceflight|
|August 10, 1965||Joseph Engle||5.20||3,550 mph (5,713 km/h)||271,000 ft (51.3 miles/82.6 km)||U.S. recognized spaceflight; Engle later piloted two space shuttle missions; first man to pilot two winged vehicles back from space|
|August 21, 1968||William Dana||5.01||3,443 mph (5,540 km/h)||267,500 ft (50.7 miles/81.5 km)||U.S. recognized spaceflight|
|October 14, 1965||Joseph Engle||5.08||3,554 mph (5,720 km/h)||266,500 ft (50.5 miles/81.2 km)||U.S. recognized spaceflight|
|November 15, 1967||Michael J. Adams||5.20||3,570 mph (5,745 km/h)||266,000 ft (50.4 miles/81.1 km)||Adams killed when X-15 broke up in flight; pilot awarded astronaut wings; U.S. recognized spaceflight|
Eleven of the 13 suborbital flights reached between 50 and 62.1 miles (80.5 and 100 km) while two flew above 62.1 miles (100 km). The eight pilots who flew the missions were awarded astronaut wings.
Joseph Walker was the only pilot to fly above 100 km; he did so twice in 1963. His second flight reached a record 354,200 ft (67.1 miles/108 km), a record for winged vehicles that would stand for 41 years until it was broken by Scaled Composites pilot Brian Binnie aboard SpaceShipOne in 2004.
Both Walker and Joseph Engle flew the X-15 above 50 miles. Engle would later to go on to fly two space shuttle missions, becoming the first astronaut to fly two different types of winged vehicles back from space.
There was one in-flight fatality in the program. On Nov. 15, 1967, Maj. Michael J. Adams lost control of an X-15 while reentering the Earth’s atmosphere after reaching an altitude of 81.1 km (50.4 miles). He was killed when the fuselage broke up and crashed in the Mojave Desert. The U.S. Air Force posthumously awarded astronaut wings to Adams.
The X-15 program ended in December 1968, having obtained a maximum speed of Mach 6.7. It was a highly successful research program that contributed valuable knowledge for the space shuttle program. It would be 35 years before anyone else would fly suborbital by design.
SpasceShipOne is an experimental winged vehicle that was dropped at high altitude by the White Knight carrier aircraft. SpaceShipTwo’s predecessor was designed and built by Burt Rutan and his team at Scaled Composites to win the $10 million Ansari X Prize as the first privately built, reusable human spacecraft capable of flying three people above 100 km (62.1 miles) twice in two weeks. Billionaire Paul Allen backed the program with $28 million.
SpaceShipOne made three flights above 100 km in 2004. Two Scaled Composites pilots, Mike Melvill and Brian Binnie, were awarded astronauts wings by the Federal Aviation Administration (FAA) for their flights.
Suborbital SpaceShipOne Flights, 2004
(Recognized as Spaceflights by FAI)
|Date||Crew||Mach||Maximum Velocity||Maximum Altitude||Notes|
|June 21, 2004||Mike Melvill||2.9||2,225 mph (3,581 km/h)||328,491 ft (62.2 miles/100.1 km)||First private suborbital spaceflight|
|September 29, 2004||Mike Melvill||2.92||2,240 mph (3,605 km/h)||337,697 ft (64 miles/102.9 km)||Second private suborbital spaceflight; first of two flights for $10 million Ansari X Prize|
|October 4, 2004||Brian Binnie||3.09||2,225 mph (3,581 km/h)||367,500 ft (69.6 miles/112 km)||Second of two flights for $10 million Ansari X Prize; highest piloted suborbital flight by a winged vehicle, breaking 41-year old record set by Joseph Walker in the X-15|
None of the flights carried passengers in the two seats located behind the pilot. SpaceShipOne carried additional mass to simulate the weight of two passengers on the Ansari X Prize flights.
Binnie set a new altitude record for winged vehicles when he flew SpaceShipOne to 69.6 miles (112 km) on the second Ansari X Prize flight. Binnie broke the 41-year old record of 67.1 miles/108 km that Joseph Walker set in the X-15 in 1963.
SpaceShipOne’s flight history consisted of 17 flights. They incluyded: six powered flights, three of which reached altitudes below 100 km (62.1 miles); eight glide flights; and three captive carry flights during which SpaceShipOne never separated from White Knight.
Rutan wanted to continue flying SpaceShipOne with passengers aboard. However, Allen had been unnerved by various close calls during the flight test program. He also had an offer to donate the vehicle to the National Air and Space Museum. So, SpaceShipOne was retired after the second Ansari X Prize flight.
Branson’s Virgin Galactic licensed the SpaceShipOne technology and partnered with Rutan’s Scaled Composites to build the larger SpaceShipTwo suborbital vehicle and WhiteKnightTwo mother ship.
Accidental Suborbital Flights
Two orbital Soyuz launches became accidental suborbital flights due to anomalies with their Soyuz boosters. The first occurred in 1975, the second in 2018.
Accidental Suborbital Flights Above 50 Km
|April 5, 1975||Vasily Lazarev, Oleg Makaron||Soyuz 18a||629,921 ft (119.3 miles/192 km)||Orbital flight to Salyut 4 space station aborted after third stage ignited with second stage still attached; highest piloted suborbital flight.|
|October 11, 2018||Alexy Ovchinin,|
|Soyuz MS-10||305,118 ft (57.8 miles/93 km)||Orbital flight to the International Space Station aborted after Soyuz rocket stage failed to separate properly from second stage; recognized as a suborbital flight by the United States but not by the FAI.|
Soviet cosmonauts Vasily Lazarev and Oleg Makaron were headed for a 60-day stay aboard the Salyut 4 space station when the third stage of their booster failed to separate from the second stage. Only three of the six locks connecting the stages released. An automated program aborted the launch, exposing the two cosmonauts to a harrowing descent during which they experienced a punishing 21.3 g (209 m/s²)
Makarov made two more Soyuz flights to the Salyut 6 space station. Lazarev never fully recovered from injuries he suffered from the flight and never flew to space again.
Russian cosmonaut Alexy Ovchinin and NASA astronaut Nick Hague suffered a much milder abort in October 2018 due to a booster separation anomaly on a Soyuz launch to the International Space Station. Neither man was injured; both would fly to the station aboard a Soyuz spacecraft in March 2019.
Suffice to say, both Soyuz crews were too busy with their separate emergencies to enjoy their brief trips to space. They were fortunate the abort systems worked and that they survived the flights.
The only other launch abort involving a crewed Soyuz spacecraft occurred in September 1983. An escape tower pulled the Soyuz T-10-1 spacecraft away from its Soyuz booster, which had caught fire on the launch pad. Soviet cosmonauts Vladimir Titov and Gennadi Strekalov were badly shaken but otherwise unharmed. Both would later fly to space.