Extract from the book: Chapter 6
An oft-reminded cautionary mantra in mountaineering circles is that more accidents happen on the descent. The same is true for spacecraft. The reasons are somewhat similar in either case. Mountaineers will point to physical fatigue, mental fatigue and overall sharplessness. It is also technically more difficult due to the higher potential for slips and falls.
In the case of spacecraft from launch to the duration of its flight in orbit it loses mechanical and electronic integrity. Mechanically the craft is subjected to high temperature and pressure variations, vibrations, stresses and micro meteorite impacts. Electronically the craft is bombarded with radiation notorious for corrupting memory and damaging logic gates. In addition the crew also fatigues, having been subjected to weightlessness for days and weeks in a cramped and awkward environment. In this condition the re-entry craft will now be subjected to extremes of pressure, temperature and G-forces, while having to simultaneously fight torques to keep it stable and enact a carefully-timed sequence of aerobraking events.
Atmospheric re-entry is an underappreciated technology. The decade of the 1960s that saw the stupendous development of manned spaceflight was also prone to witnessing the maximum casualties and failures during re-entry.
Landing in Trouble
On the maiden voyage of human spaceflight Gagarin's Vostok 1 did not come down smoothly. A long kept secret by the Soviet government was that Yuri Gagarin's descent had its share of malfunctions and heart stoppers. Some would consider him lucky to have landed safely. After the retrorockets fired to initiate re-entry, in about 8-10 sec the descent module that housed him was to separate from the instrument section which was now expendable.137 The separation mechanism however malfunctioned causing both the modules to be attached by cables. The uncalculated mass also caused the two modules to go into a spin. The Vostok descent module finally separated a full harrowing 10 minutes late. Gagarin landed 300 km off target and not before a little more drama as his reserve parachute partially deployed along with the primary one.138
It must be noted that Gagarin did not land in his spacecraft but instead ejected and parachuted down. The Soviets had tested module landing with dogs before but felt it not reliable enough for manned flights at the time. This too was a point of contention as it did not satisfy international standards for an aerospace record which required the passenger to take off and land in the same vehicle and was kept secret by the Soviet government.139 The second Soviet in space Gherman Titov also had a harrowing experience at re-entry as the instrument section did not fully disentangle until the connecting straps finally burnt away in the atmosphere.
The Voskhod 2 mission which boasted of the first spacewalk (1965) failed to fire its automatic retrorockets for de-orbit, forcing the decision to go into manual re-entry and for the controllers needing to work out the landing data.140 The ship finally landed nearly 400 km north of its target and the cosmonauts had to spend the night in snow and cold because they landed in a dense part of the Taiga which had made it impossible for helicopters to land nearby.
The first fatality on a space mission would be the death of cosmonaut Vladimir Komarov on a Soyuz-1 re-entry in April 1967. The Soyuz-1 was notoriously plagued with glitches and the re-entry problems started right from the non-firing of the retrorockets on time, to the entangling and meshing of cables, a spinning module and the final nail in the coffin was the non-deployment of its parachute. Resident farmers in the Orsk area reported that the ship had fallen to Earth with great speed and that the parachute was turning, and not filled with air.141
Without any means of braking, the ship plummeted and hit the ground at 40 m/s. And if that was not enough, the soft-landing engines which were designed to break the fall at touchdown detonated after the crash, blowing up 30 kg of concentrated hydrogen peroxide.142 Famous World War II pilot and one of the most accomplished test pilots in the Soviet Union, Sergey Anokhin, had this to say, “I can’t tell you how many burned up airplanes I saw during the war, but there is no comparison with what we saw there…”.143 During the descent Komarov had complained, “This devil ship! Nothing I lay my hands on works properly”.144
The next tragedy to hit the Soviet space program was the loss of crew during re-entry of the Soyuz-11 (Jan 1971). It was the first successful manned mission to a space station (Salyut 1) and was also the record longest manned space mission (23 days) at the time. A leaking ventilation valve caused rapid depressurization of the capsule. The search and rescue team did not expect to find lifeless bodies on opening the hatch.
The three cosmonauts had asphyxiated and ‘depressurized’ – blood in the lungs, nitrogen in the blood and haemorrhage in the brain.145 There was a wide belief in the space program that this could have been averted if the cosmonauts had the presence of mind to locate the hissing leak and block it, even with a finger. However, fatigued after three weeks in space, on a bumpy ride home, with a pressure drop from normal to zero in 112 seconds – all easier said than done.
The USA too had its hiccups right from their early days. After splashdown the hatch bolts of the Mercury Liberty Bell 7 (July 1961) mysteriously exploded prematurely at sea, causing water to fill the capsule. Astronaut Gus Grissom would have drowned were it not for his quick reaction to evacuate the capsule in time. During Armstrong’s first trip into space aboard the Gemini 8 (March 1966) there was the need for an emergency landing, forcing them to land in the wrong ocean.146 The latest disaster was during re-entry of the Space Shuttle Columbia in 2003 which lost all seven crew members. This was a glided re-entry, not a ballistic re-entry as were the others.
Today, Russia is the undisputed technology leader in manned re-entry, and they have had an outstanding record over the past three decades. The Chinese manned program including the re-entry is derived from Soviet technology. NASA has not performed a manned ballistic re-entry since the Apollo missions.
Threading a Needle
The core principle behind manned atmospheric re-entry is to somehow offload the vehicle’s enormous Kinetic Energy (K.E.) through the dissipation of heat; and in the process bring its velocity down to subsonic levels such that the parachute can deploy at a safe height in the lower atmosphere.
From low-Earth orbit (LEO) that translates to a speed change from ~8 km/s to a safe 200 m/s for parachute deployment, or a reduction in speed of 97.5%. However, because the K.E. is correlated to the square of the velocity, the needed reduction in K.E. is a slightly more daunting 99.999%. Consider a manned return capsule of mass 3000 kg. At 8 km/s this translates to a K.E. (1/2 mv2) of 96,000 MJ, which needs to be shed. The bulk of the speed reduction happens in about 10 min or 600 s. This translates to a power output of 160 MW or 214 KHp or 214,000 horses pulling it in the opposite direction for 10 minutes in order to get it to stop.
The blunt design of the capsule prevents air from getting out of the way aerodynamically thus creating a barrier, and this barrier in collision with the oncoming air produces a shockwave – a plasma sheath of high temperature (~6000°C) and high pressure, which fortunately protects the capsule from incineration and mechanical damage. Due to the high deceleration, the crew will also experience forces in the 10-15g range under normal operation.
The shockwave is useful as it creates a high pressure high temperature buffer layer and this wave ‘extends a considerable distance into the atmosphere on either side of the body, leaving a broad wake of heated gas that contains a major portion of the total heat load’.147 The blunt nose is designed to maximise heat dissipation to the atmosphere. However even so it cannot prevent the capsule body temperatures to heat up to about 1600°C (through friction and convection). The ablative materials protecting the capsule come in handy by absorbing heat and melting away as needed.
Fig 6.2a Capsule atmospheric re-entry and shock wave underneath (artist’s impression)
If the entry is too steep (undershooting), there will be more dangerous G forces on the crew and the heating of the capsule could go beyond the ablative shield’s limit and jeopardize the crew. In the case where the entry is too shallow (overshooting) the crew will land beyond their landing area, possibly in hostile territory or on a terrain not suitable for the capsule, like land for a water-based return. This gives rise to the term ‘entry corridor’, a narrow region of the space/atmosphere interface through which the capsule must enter for a safe landing. Hitting the entry corridor from orbit should not be very daunting. Simply because the satellite has a predictable trajectory having been rigorously tracked after its many revolutions around Earth.
Also if, at a certain re-entry initiation point, the parameters are not ideal, the controllers can wait for any number of the following cycles depending on the fuel. This has occurred on multiple occasions for both the US and USSR. The most notorious such incident was that of astronaut Scott Carpenter who aboard the Aurora 7 (24 May 1962) intentionally missed his re-entry point and went on to cover his low fuel warning with a piece of tape so it wouldn’t bother him.148
Amongst the reasons for his postponed re-entry was the search for 'fireflies' which others had seen on earlier flights. He landed dangerously low on fuel and was recovered 250 miles from the intended landing point, floating in a life raft and eating a candy bar.149 Ground control was not pleased and it was to be his last flight in space. Later on, craft were generally stocked for three days of shortage and that translates to about 50 extra orbits. Within these seemingly magnanimous boundaries, the world space programs still had an atrocious record on re-entry accuracy and subsequent safety throughout the 1960s.
Fig 6.2b Typical US pre-Apollo re-entry profile
Returning from the Moon however, is a completely different and far more complex beast.
Let us first consider the Kinetic Energy. On its return trip from outside the clutches of Earth’s gravity, the craft’s speed will be equal to about Earth’s escape velocity of 11.2 km/s. The same 3000 kg capsule will now be energized at 188,160 MJ and the heat output during the fall will need to be at a rate of about 314 MW or 421 KHp. That’s an extra 200,000 horses kicking and neighing to stop this thing than were needed from LEO.
The size of the feasible corridor of entry thus gets much smaller and the penalty for error is exponentially increased. In the words of Nikolai Kamanin, head of cosmonaut training in the Soviet space program, when summarizing the journey back of the Zond-5,
“The spacecraft, according to estimates, should enter the atmosphere at an angle of 5-6 degrees to the local horizon. Even minus one degree in the re-entry angle would mean the Earth’s atmosphere would fail to 'catch' the spacecraft. Even one more would increase the G-load by 10-16 units above the estimated 30-40 units, and a greater angle would be dangerous not only for the crew, but may also destroy the spacecraft. In other words, the spacecraft should fly over 800,000 kilometres along the Earth-Moon-Earth route and at a speed of 11 km/s hit the zone ('funnel') of safe entry 13 km in diameter. Such high precision can be compared only to that of hitting a one-Kopeck coin from a 600m distance”.150
Hence for a returning Moon mission not only are the margins of error razor thin, the stakes are much higher. A bit of an undershoot, and the crew will be subjected to fatal G forces and the craft to unbearable thermal and mechanical stresses. A bit of an overshoot, and the craft could ‘miss’ the Earth and be sent on a wild elliptic orbit in deep space. And importantly, unlike a LEO return, there is only one chance to get it right.
Fig 6.2d Re-entry corridor
The sheer difficulty in reliably performing ballistic re-entry from deep space especially with biological payload is why skip re-entry was developed. Skip re-entry is a technique whereby the landing module is designed and oriented to create aerodynamic lift such that it leaves the atmosphere and re-enters again for its final entry. The purpose is to reduce speed more gradually and thus reduce the peak G force on the crew and peak heat and stress on the spaceship. The tradeoff is a longer range from re-entry initiation to the landing point. This in turn can amplify errors through external variables like weather. Additionally, there are now two plasma blackout periods, one on the first dip and the other on the final re-entry.
The first attempt at skip re-entry for a biological payload rated return capsule was the Zond-4 (11 March 1968), which after a lunar flyby on re-entry was not able to skip back out into space causing it to go in ballistically. The ensuing G forces would have killed human occupants. The now shortened re-entry range necessitated a landing area over Africa, and this in turn activated a pre-armed explosive destruct system called APO. APO was activated over the Gulf of Guinea near the west coast of Africa.151 The APO served to prevent technology leakage as well as to conceal Soviet failures.152
The next attempt was the famous Zond-5 (21 Sept 1968), the first instance of earthlings on a circumlunar mission. Here too the skip re-entry mechanisms had failed but were detected early enough for a more controlled ballistic re-entry with a landing in the Indian Ocean from where they would transport the vehicle to friendly Bombay and then back to Moscow. Human payload would have unlikely survived the 40G of deceleration.
The first correct demonstration of skip re-entry was the Zond-6 on 17 November 1968 which
“Entered its tiny entry corridor into Earth’s atmosphere at a velocity of 11.2 km/s. Passing through its 9000 km long entry corridor it skipped out of the atmosphere, having reduced its velocity to 7.6 km/s, and began a second re-entry that further lowered velocity to only 200 m/s. Throughout the re-entry, engines on the descent apparatus automatically fired to vary roll control so as to change lift force and reduce G-loads. Unlike its predecessor, the Zond-6 descent apparatus was subjected to a maximum of four to seven Gs. The complex re-entry was a remarkable demonstration of the precision of the L1 re-entry profile”.153
Alas, a faulty gasket caused a leak which depressurized the capsule killing all the biological specimens.
Fig 6.2d Skip Re-entry
Amongst the greatest feats of wizardry is how NASA hoodwinked the world into believing that on 21 December 1968, the agency successfully brought home a mammoth 3-man astronaut crew (Apollo 8) from the Moon; that too on their first such demonstration, and without testing it on guinea pigs before.
The literature surrounding Apollo’s re-entry methods are understandably ambiguous. When in doubt, mumble. There are three different versions of how Apollo re-entered, depending on who you ask.154 Apollo flight director Chris Kraft has stated that Apollo used a skip re-entry; the astronauts at Johnson Space Center in 2011 described it as a direct entry; and some experts qualify the Apollo direct entry as a ‘double dip’ (Kaya, 2008).
It is also a testimony of the unquestionable prestige and power that NASA wielded in the 1960s and 1970s. That edifice crumbles every day. At the time of writing NASA does not have the capability to bring back its own astronauts from the International Space Station, let alone from beyond LEO.
The Curious Case of Qantas Flight 596
Passengers and crew aboard the Qantas 596, Boeing 707 Flight from Brisbane to Honolulu in the wee hours of 25 July 1969 were treated to the live view of the Apollo 11 capsule’s re-entry. A truly spectacular and a once-in-many-a-lifetime event. The episode was described in the Sydney Sun Herald Newspaper, page 24, Sunday 27 July 1969.
Boeing saw re-entry spectacle
by Helen Styles
Captain F.A. Brown, Qantas 707 pilot, yesterday described the awesome sight of the Apollo 11 moon capsule’s re-entry into the atmosphere early on Friday.
Captain Brown had just returned from Honolulu after he had piloted a flight that passed within 450 miles of the returning space capsule.
The fiery, disintegrating service module, from which the command module occupied by the astronauts had already separated exploded into a flare that lit up the darkness over the Pacific ocean near the Gilbert and Ellice Islands like daylight, he said.
The incandescent command module containing the astronauts showed a tail of points of yellow light from the heat shield particules, as it sped by during entry into the top of the atmosphere, 66 miles above earth.
The spectacle was seen by the 82 passengers and 13 crew members aboard the airliner.
Captain Brown said the departure of the Boeing 707 on a flight from Brisbane to Hawaii had been put back 3 hours 19 minutes on advice from NASA experts so the re-entry could be witnessed on a parallel flight track at a safe distance from the space vehicle.
The capsule’s re-entry track was on an elliptical curve 1, 300 miles long.
The capsule re-entered the atmosphere at 25,000 m.p.h. and splashed down 1000 miles away from the plane, its speed slowed to 15 m.p.h. by parachutes. Captain Brown said.
From the point of re-entry to splashdown took 14 minutes.
“The module was in our vision for 3 minutes 46 seconds,” Captain Brown said.
Fig 6.3 Sydney Sun Herald Newspaper, page 24, Sunday 27 July, 1969
Another fascinating description was in The West Australian on Saturday, 26 July 1969, page 12:
A Bird’s Eye View of the Return
Passengers on a Qantas flight from Brisbane to Honolulu early today had a bird’s eye view of the Apollo 11’s re-entry into the earth’s atmosphere.
The pilot of the jet, Capt. Frank A. Brown, gave a running commentary on the scene. It was relayed to radio stations throughout Australia.155
Capt. Brown began his description when the plane was flying at 39,000ft over Gilbert and Ellice Islands in the mid-Pacific.
“There’s a little cloud above us but we are going to get a perfect view of Apollo 11,” he told the 82 excited passengers.
“We have about two minutes to go, the capsule is about 500 miles from earth now. It has just crossed the east coast of Australia above Mackay, Queensland.”
“The astronauts are travelling at six miles a second. A staggering speed, isn’t it?”
“We expect to see an object behind us in just over a minute and a half. It will be brighter than a bright star”
“At that time it will be something like 500 miles away.”
A good view
Capt. Brown asked the passengers to move to the left side of the plane and requested them to share windows to get a good view.
Then he shouted: “Here they come on the left, one object brighter than the other. See the two of them, one above the other. One is the command module, the other is the service module. They both weigh six tons.”
“They are picking up heat now. The bottom one is leaving an incandescent descent trail. See it flashing. See the trail behind them – what a spectacle. You can see the bits flying off. Notice that the top one is almost unchanged while the bottom one is shattering into pieces. The part that is disintegrating is the rocket service module, the top one is the command module.”
“It looks like a pretty normal re-entry. Mathematically that seems perfectly sound and the timing is correct. It looks real good to me.”
“In my opinion that was the spectacle of a lifetime”
After the re-entry the passengers celebrated with champagne and Capt. Brown presented them with certificates bearing a reproduction of the medallion left on the moon by Armstrong and Aldrin.
– Cable Services
Captain Frank Brown flew 138 and 338 series Boeing 707s for Qantas in the 1960s and early '70s, and it is worth noting that his hobby was orbital mechanics and satellite trajectories. So much so that "Qantas often used to schedule Frank around NASA’s Mercury, Gemini and Apollo programs and Frank could usually arrange to get his Boeing into the dress circle, so his passengers could watch a launch or recovery”.156
This would explain his surprisingly knowledgeable commentary on the Apollo 11 re-entry. Of course he did have help from NASA knowledge experts, after all why would his Brisbane to Honolulu flight have been “put back 3 hrs 19 min on advice from NASA experts so the re-entry could be witnessed on a parallel flight track at a safe distance from the space vehicle”.
Captain Frank Brown’s live commentary makes it easy to deconstruct Apollo’s re-entry trajectory, and from it, it is easy to see that the re-entry profile is direct ballistic. There is no form of skip whatsoever, or even an elongated path along the atmosphere. It is also easy to see that the Apollo re-entries followed the same path and splash location as its predecessors, the Mercury and Gemini missions.
Eastbound launches from Cape Canaveral Florida follow the path of crossing Africa from the NW to the SE, and then re-climbing from the SW to the NE over Australia, and then on towards Hawaii on their way back to the Cape Canaveral area in America. Due to the USA’s strong naval presence around Hawaii, it has traditionally been a preferred ocean landing area for their manned flights. This further adds credence (if it is still needed) that the Apollo missions were routine LEO voyages. All Apollo missions landed near Hawaii following the familiar trajectory over Australia. Wouldn’t one expect lunar returning modules to have different trajectories as was the case with the Soviet missions?
Fig 6.3a Flight path for launches from Cape Canaveral – 3D view
Fig 6.3b Flight-path for launches from Cape Canaveral – map view
Fig 6.3c Flight path of the re-entry of Apollo 11 and the Qantas Flight 596
The Qantas 596 flight was travelling from Brisbane to Honolulu on a track parallel and south east to the Apollo trajectory, which is why they were advised to go to the left side of the plane to see the return module. A couple of minutes before re-entry as mentioned the spacecraft crossed over Mackay, Queensland which is about 1000 km north of Brisbane. Once the return capsule is in sight, the Captain says, “it will be something like 500 miles (~800 km) away”. This too makes sense because at the time they are at an altitude of 39,000 ft (~12 km), and that is roughly the maximum distance one’s line of sight will be at that height. Once the craft enters the atmosphere Capt. Brown clearly describes the burning and disintegration of the service module. At this point the flight is over the Gilbert and Ellice Islands, just beyond halfway from the Australian coastline and Hawaii.
This also clearly shows that this could not be a skip re-entry, or else the service module would have already disengaged and burnt up on the first atmospheric entry itself. He says the capsule’s re-entry track was on an “elliptical curve 1300 miles long” – exactly what one would expect on a direct ballistic re-entry. A skip or a ‘double dip’ would be much more elongated. The Captain also remarks that the "capsule re-entered the atmosphere at 25,000 m.p.h. (11.2 km/s)", which is the speed of re-entry from deep space. Now we know it would be impossible to land a craft from that speed in such a short elliptic arc without incinerating the craft. But that is the information he was given and so relayed.
In fact Capt. Brown says so himself, “It looks to me like a pretty normal re-entry. Mathematically that seems perfectly sound and the timing is correct. It looks real good to me”. These are the words of a man speaking from experience and comparing past notes – from the Mercury and Gemini missions.
Yes Captain, it was a normal re-entry, from low-Earth orbit.
Extract ©2020 Garvit Rawat
138 Declassified documents offer a new perspective on Yuri Gagarin’s flight; by Asif Siddiqi; www.thespacereview.com; The Space Review; Oct 12, 2015
139 Sputnik and the Soviet Space Challenge; Asif A. Siddiqi; p.283
140 Ibid., p.458
141 Ibid., pp.587-589
143 Rockets and People, Vol. III; Boris Chertok, p.646
144 Starman; by Jamie Doran, Piers Bizony; p.199
145 The Soviet Space Race with Apollo; Asif A. Siddiqi; p.781
146 Neil Armstrong’s Forgotten First Space Flight; Josh Gelernter; April 16, 2016; nationalreview.com
147 Re-entry and Planetary Entry; W.H.T. Loh, 1968; p.2
148 “Mercury Astronaut Scott Carpenter and the Controversy Surrounding Aurora 7”; Amy ShiraTeital; Oct 13, 2013; Popular Science (popsci.com)
149 Moon Shot; Alan Shepard and Deke Slayton; pp.144-145
150 Kamanin, “A Goal Worth Working for”, p.10; Translation: Soviet Space Race with Apollo; Siddiqi, Asif A., p.656
151 The Soviet Space Race with Apollo; Asif A. Siddiqi; p.618
152 Rockets and People, Vol. 3; Boris Chertok; p.710
153 The Soviet Space Race with Apollo; Asif A. Siddiqi; p.664
154 Re-Entry Matters, A Detailed Investigation into Apollo Command Module Returns; Mary Bennett; aulis.com/re-entrymatters
155 The audiofiles of Capt. Frank Brown’s telling of the Apollo 11 re-entry from aboard the plane are available at honeysucklecreek.net; The Honeysuckle Creek Tracking Station, near Canberra was set up by NASA in 1967 to support the Apollo mission; honeysucklecreek.net; The Boniecki Tapes; www.honeysucklecreek.net/msfn_missions/Apollo_11_mission/index.html
156 Best Seat in the House; John McHarg; May 31, 2016; aviatormag.com.au
About the Author
Garvit Rawat was educated at The Doon School, Dehradun, India. He has a Bachelors degree in Mechanical Engineering and a Masters in Information Systems (2001) from the Birla Institute of Technology and Sciences (BITS), Pilani.
He also has an MBA from the University of Toronto, specializing in Operations and Strategy (2009). Garvit Rawat works in Industrial maintenance and manufacturing. He lives in Toronto, Canada.
This is an extract from his first book available on Amazon.