With the start of the Apollo program in 1960, a wide range of technologies and techniques needed to be developed to mount advanced missions beyond Earth orbit. Among these was figuring out how to safely return the Command Module (CM) to Earth from the Moon. At this point in time, NASA and branches of the military had practical experience with spacecraft and warhead-laden reentry vehicles hitting the Earth’s atmosphere to speeds as great as about 7,000 meters per second. But Apollo would be reentering the Earth’s atmosphere at a much higher 11,300 meters per second involving kinetic energies over twice that of a spacecraft returning from low Earth orbit.
While one could extrapolate from current experience to estimate the heat loads involved, there were different results depending on the methods used. The uncertainties in this new environmental regime needed to be addressed in order to ensure the spacecraft (and its passengers!) were properly protected without an undue mass penalty. In order to resolve these issues, NASA started Project FIRE (Flight Investigation Reentry Environment).
Origin of Project FIRE
In September of 1960, NASA personnel at Langley Research Center (which had responsibility for Project Mercury – see “The Origins of NASA’s Mercury Program”) proposed launching a series of four reentry vehicles each using the then-new Atlas-Agena B rocket to test conditions for high-speed reentry into the Earth’s atmosphere from the Moon or beyond. The reentry vehicles would be constructed of Mercury spacecraft components and would give Project Mercury personnel additional experience in tracking and data acquisition procedures as well as provide vital data for future spacecraft design.
Langley’s original proposal to use the new Atlas-Agena B, shown here in its first launch of MIDAS 3 in July 1961, to launch payloads to study high-speed reentry. (USAF)
This proposal was abandoned in 1961 in favor of a new one initially dubbed Project FIARE (Flight Investigation of Apollo Reentry Environment) – although another name proposed by NASA management in September 1961, Project Calorie, never caught on. In August 1961, the proposed plan was to launch four sub-scale models of the Apollo CM shape using the Atlas-Agena B as a launch vehicle for each mission. The reentry vehicles would be fitted with beryllium calorimeter heat shields to make direct measurements of the heat loads during a high-speed reentry.
On February 18, 1962 NASA officially announced plans for a modified program known as Project FIRE (Flight Investigation Reentry Environment). Instead of using the relatively expensive Atlas-Agena B, Project FIRE would employ modified Atlas-D ICBMs built by General Dynamics to launch a “reentry package” on a suborbital ballistic trajectory. The reentry package would then use a solid rocket-based “velocity package” to accelerate the Apollo CM model to a speed of about 11,300 meters per second during the return leg of the trajectory for the reentry test. Just two launches in the 1963-64 timeframe were planned instead of the originally proposed four flights to help reduce costs further. The project, directed by NASA’s Office of Advanced Research and Technology, would be managed by Langley. On March 29, 1962, NASA named Republic Aviation as the prime contractor for the reentry package and Chance Vought as the contractor for the velocity package. On November 20, NASA named General Dynamics as the contractor responsible for systems integration.
Diagram showing the configuration of the Atlas-Antares II launch vehicle selected for Project FIRE. Click on image to enlarge. (NASA)
The objectives of Project FIRE included measuring the radiative and conductive heat transfer to the reentry package as well as radiant energy and spectral data of the hot gas cap just ahead of the reentering body. Secondary objectives included measuring the response of heat shield materials and measuring radio attenuation effects during the reentry blackout period. In addition to the actual flight tests, Project FIRE would also perform a series of ground-based tests using the Unitary Plan Wind Tunnel, the 2.4-meter High Temperature Tunnel and the 2.7 by 1.8-meter Thermal Structures Tunnel at Langley.
A model of the Project FIRE reentry package being prepared for wind tunnel testing at Langley Research Center. (NASA/LaRC)
Mission Hardware & Mission Profile
The Atlas D boosters used for Project FIRE were “thick skinned” versions like those employed for Project Mercury designed to carry heavier payloads than the standard ICBM variant of the missile. Producing 1,633 kilonewtons of thrust at launch using its Rocketdyne-built MA-5 propulsion package (consisting of the pair of booster engines and single sustainer), the 123 metric ton rocket would loft its payload on a high-apogee ballistic path.
Cutaway diagram of the Project FIRE payload. Click on image to enlarge. (NASA)
The payload, which would be protected beneath a clamshell fairing during ascent, consisted of a velocity package and a reentry package with a total height of 3.66 meters and a mass of about two metric tons. At the heart of the 1,905-kilogram velocity package was an Antares A5 solid rocket motor (sometimes known as the X-259 or Antares II) manufactured by the Allegany Ballistics Laboratory similar to the version used as the third stage of the all-solid Scout launch vehicle. This 1,273-kilogram motor would produce 61 kilonewtons of thrust for 30 seconds. Also included in the velocity package was a shell which physically connected the motor to the Atlas launch vehicle. This shell housed an attitude control and stabilization system similar to that employed on the Scout which used six cold gas jets as well as a set of three rockets to spin up the Antares rocket and the reentry package for stability prior to ignition.
Exploded view of the Project FIRE spacecraft carried on top of a modified Atlas-D. Click on image to enlarge. (NASA)
The 83-kilogram reentry package was attached to the velocity package by a 24-kilogram adapter which also include a pair of small separation rockets. The reentry package was a cone with a base diameter of 66 centimeters and a height of 53 centimeters – about a one-sixth scale analog of the Apollo CM. The heat shield for the reentry package consisted of three beryllium calorimeters interleaved with phenolic asbestos layers for insulation which would be jettisoned one after the other on command during reentry in order to get accurate heat load readings from a fresh heatsink during three key phases of the descent. The reentry package included 258 thermocouples, a pair of radiometers to measure total radiant energy and a telemetry system which would broadcast data in real time as well as a tape-delayed system to transmit data collected during the radio blackout during reentry. Data from the reentry package would be supplemented by ground and air-based observations of the reentry under clear-sky nighttime conditions. No recovery of the reentry package was planned.
Cross section of the Project FIRE reentry package. Click on image to enlarge. (NASA)
A typical mission would start with a launch of the Atlas-Antares II rocket from Launch Complex 12 (LC-12) at Cape Kennedy (which reverted to its original name of Cape Canaveral in 1973) with the rocket and its payload flying down the Atlantic Missile Range. After about five minutes of powered flight, the Atlas’ sustainer engine would shutdown followed seconds later by the vernier engines which would trim the ascending rocket’s trajectory. This would be followed by the jettisoning of the launch shroud then spacecraft separation at an altitude of about 305 kilometers some 790 kilometers downrange. In order to avoid recontact with the spacecraft, the Atlas would fire a set of retrorockets to increase the separation rate further. The velocity package would use its cold gas jets to set and maintain its attitude for the reentry to come. The velocity package would reach an apogee of about 800 kilometers around 3,900 kilometers downrange after 15 minutes of flight.
Schematic diagram of a typical Project FIRE mission. Click on image to enlarge. (NASA)
After a 21-minute coast following Atlas shutdown, a fast-paced series of events would take place to accelerate the reentry package to the required speed. The three spin rockets on the velocity package shell would be ignited by a timer about 25 minutes and 45 seconds after launch to spin up the Antares rocket and reentry body to 180 RPM. Three seconds later the velocity package shell is jettisoned followed three seconds later by the ignition of the Antares rocket motor. After about 27 minutes of flight, the spent Antares rocket separates from the reentry body using a spring loaded device producing a relative velocity of about two meters per second. This would be followed six seconds later by the firing of a pair of small rockets on the adapter to send the velocity package into a tumble which would increase drag and further increase the separation rate.
Exploded view of the Project FIRE reentry package showing the calorimeters and heat shields which would be ejected during reentry. Click on image to enlarge. (NASA)
The reentry package would reach its atmospheric interface at an altitude of 122 kilometers travelling about 11,300 meters per second in a direction 15° below the local horizontal. The descending reentry package would transmit its findings in real-time to a station on Ascension Island in the South Atlantic where other ground-based observers would be located. The University of Michigan was responsible for launching a 29-kilogram payload on a Nike-Apache sounding rocket shortly after reentry to provide in situ measurements of upper atmospheric properties to an altitude of 120 kilometers to be used in interpreting the Project FIRE’s reentry results. Following the end of the reentry communications blackout, recorded data would be transmitted to the ground down to an altitude of about 4.6 kilometers followed by the impact of the reentry package in the Atlantic about 8,250 kilometers downrange after a flight of about 32 minutes.
FIRE I
The first flight test of Project FIRE used Atlas 263D as the booster for the Atlas-Antares II launch vehicle. It arrived at Cape Kennedy on August 28, 1963 following its acceptance by the USAF. After a post-shipment checkout, Atlas 263D was erected at LC-12 on August 30 for a preflight checkout. Afterwards, the Atlas was removed from LC-12 and placed into storage at Hanger J on October 4. With an April launch window for the FIRE I mission set, Atlas 263D was removed from storage on March 3, 1964 and erected for the last time at LC-12. The 1,996-kilogram FIRE I spacecraft, consisting of the velocity and reentry packages, was mated with the Atlas on March 18 for final checkout.
Atlas 263D shown after its delivery on August 28, 1963 for use in the first Project FIRE mission. (General Dynamics/SDASM)
With a successful simulated launch completed on April 3, 1964, all was ready for a launch attempt on April 6. Unfortunately, bad weather downrange forced the date to be passed over before the countdown even began. The four-hour (plus scheduled holds) countdown for the first actual launch attempt started at 10:31 AM EST on April 10. The countdown proceeded largely without incident with only one unscheduled hold to attend to an Atlas battery issue. Problems with Atlas telemetry forced a hold at 11:00 PM EST with the countdown at the T-10 minute mark. But by 11:12 PM EST, the launch was scrubbed due to the telemetry and weather issues downrange.
View of Atlas 263D with the first Project FIRE payload on the pad at LC-12. (NASA)
The countdown for the second launch attempt of FIRE I started at 11:20 AM EST on April 13 but the launch was scrubbed at 7:45 PM EST with the clock at the T-40 minute mark because of a problem with the Atlas sustainer engine protective boot followed by spacecraft instrumentation issues which could not be fixed within the launch window. The third launch attempt the following day, with the countdown once again starting at 11:20 AM EST, finally succeeded with liftoff from LC-12 taking place at 4:42:25.5 PM EST on April 14.
The launch of the of FIRE I from LC-12 at Cape Kennedy on April 14, 1964. (General Dynamics/SDASM)
A near-perfect performance of Atlas 263D was followed by spacecraft separation just three seconds later than planned at 5 minutes and 11.5 seconds after launch. The FIRE I payload reached a peak altitude of about 838 kilometers some 15 minutes and 50 seconds after launch before beginning its long descent back to Earth. After 26 minutes, 14.3 seconds of flight, the spin motors on the velocity package shell fired followed three seconds later by shell separation. Three seconds after that, the Antares II rocket motor ignited at an altitude of 299.4 kilometers and burned out after 32.8 seconds.
The descent trajectory over the South Atlantic of the first Project Fire mission. Click on image to enlarge. (NASA)
At the 27 minute, 20.2 second mark of the flight, the reentry package separated from the now spent Antares motor. After 6.9 seconds, the reentry package reached its atmospheric interface 122 kilometers above the Atlantic travelling 11,574 meters per second at an angle of 14.6° below the local horizontal 8,046 kilometers downrange. With the g-forces building, the first heat shield ejection was commanded 22.2 seconds after entry interface followed by the second heat shield ejection seven seconds later. With the communications blackout ending 28 minutes and 6.8 seconds after launch, the quickly falling reentry package began transmitting its recorded data a couple of seconds later. Peak temperatures during reentry had reached 11,130° C. Impact came just a few seconds earlier than planned after a flight lasting 32 minutes, 45.7 seconds. Except for a roll rate gyro failure during the flight (which would complicate data analysis), the mission met all of its objectives providing first of its kind data for the fastest reentry by a manmade object to date.
FIRE II
As engineers and scientists started going through the data returned by the FIRE I flight, NASA informed the project’s contractors in the summer of 1964 that preparations for the second flight of the project could proceed. The booster for FIRE II, Atlas 264D, arrived at Cape Kennedy on March 2, 1965. Following a post-shipment checkout, the Atlas was erected at LC-12 on April 6. This was followed by the mating of the second Project FIRE spacecraft. With a mass of 2,006 kilograms, this second spacecraft was essentially identical to the first save for modifications made to the radiometers and the inclusion of additional pressure sensors. The times that the heat shields would be jettisoned was also altered so that data from slightly different parts of the reentry could be obtained.
The second Project FIRE reentry package being prepared for launch. (NASA)
The launch window for the first attempt extended from 5:14 to 11:29 PM EST on May 4, 1965 with additional daily opportunities available through May 8. If these attempts were missed, additional windows for FIRE II existed from May 21 through June 6. The countdown for the first launch attempt started at 12:20 PM EST on May 4. Except for a problem forcing the replacement of the Atlas sustainer hydraulic pump only ten minutes into the countdown, the countdown only encountered minor problems until the preplanned one-hour hold started at 5:15 PM EST at the T-45 minute mark. Unfortunately bad weather downrange forced a scrub at 6:24 PM EST. Likewise, the launch attempt the next day was called off at 9:28 PM EST due to downrange weather issues.
Atlas 264D being prepared at LC-12 to launch the second Project FIRE mission. (NASA)
With the first set of launch windows missed in early May, the third launch attempt for the FIRE II mission was made on May 21 but once again the launch was aborted at 2:11 PM EST due to poor downrange weather. With the launch recycled to the next day, the countdown started at 10:22 AM EST and proceeded towards the planned hold at the T-45 minute mark. After a 93-minute extension of the scheduled one-hour hold, the weather downrange cleared allowing liftoff to occur at 4:54:59.7 PM EST on May 22.
The launch of NASA’s FIRE II mission from LC-12 on May 22, 1965. (NASA)
Like it predecessor, Atlas 264D performed nearly perfectly save for a longer than expected burn of its vernier engines. An onboard timer commanded separation of the FIRE II spacecraft from its spent booster 5 minutes and 10.3 seconds after launch. The attitude control system then started its pitch program aligning the spacecraft to its proper attitude 7 minutes and 15 seconds after launch. The FIRE II payload reached an altitude of about 818 kilometers around 15 minutes and 20 seconds after launch before beginning its descent. After 25 minutes, 45 seconds of flight, the spin motors on the velocity package shell fired followed three seconds later by shell separation. Some 3.3 seconds after that, the Antares II rocket motor ignited at an altitude of 299.9 kilometers and burned out 31.7 seconds later.
At the 26 minute, 50.4 second mark of the flight, the FIRE II reentry package separated from the Antares motor and 7.3 seconds later reached its reentry interface at an altitude of 122 kilometers. At this point, the reentry package was travelling 11,350 meters per second at an angle of 14.7° below the local horizontal 7,884 kilometers downrange. During the punishing reentry, the first heat shield ejection was commanded 24.4 seconds after entry interface followed by the second heat shield ejection 5.4 seconds later after the peak temperature had reached 10,934° C. After the communications blackout ended 27 minutes and 35.1 seconds after launch, the reentry package began transmitting its recorded data six seconds later. Impact in the South Atlantic happened 8,256 kilometers downrange after a flight lasting 32 minutes, 14.3 seconds. There were no significant performance issues with the flight hardware and once again, all mission objectives were met.
A labelled photograph showing the reentry of the second Project FIRE payload over the South Atlantic. Time marks are in seconds after launch. Click on image to enlarge. (NASA)
With this second flight of Project FIRE validating the measurements of the first mission flown 13 months earlier, the project had met its objectives. Although the data from Project FIRE indicated that the reentry heat load for Apollo was somewhat lower than predicted, engineers erred on the side of caution and overdesigned the Apollo CM’s 680-kilogram heat shield. In the end, the Apollo Moon missions only eroded 20% of the available ablator leaving a more than ample safety margin. With a proposal to fly more advanced missions at faster velocities typical of a return from interplanetary space gone unfunded by NASA headquarters, Project FIRE was concluded. The first high-speed reentry test of the Apollo CM on the unmanned Apollo 4 mission in November 1967 verified that the design could safely return the spacecraft to Earth (see “Apollo 4: The First Flight of the Saturn V”).
A view of the Apollo 4 CM being recovered following its successful reentry and splashdown on November 9, 1967. (NASA)
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Related Videos
Here is an excellent documentary about Project FIRE and its initial flight
Here is a brief video about the FIRE II flight:
Related Reading
Additional articles on the Apollo program can be found on the Apollo page.
General References
Linda Neuman Ezell, NASA Historical Data Book Volume II: Programs and Projects 1958-1968, NASA SP-4012, 1988
Roger D. Launius and Dennis R. Jenkins, Coming Home: Reentry and Recovery from Space, NASA SP-2011-153, 2011
John H. Lewis, Jr. and William I. Scallion, Flight Parameters and Vehicle Performance for Project FIRE Flight II, Launched May 22, 1965, NASA Technical Note TN D-3569, August 1966
Project FIRE Integrated Post Flight Evaluation Report – Flight No. 1, NASA Langley Research Center Report No. GDC BKF64-018, October 30, 1964
Project FIRE, NASA Press Release 65-131, April 28, 1965
Project FIRE Integrated Post Flight Evaluation Report – Flight No. II, NASA Langley Research Center Report No. GDC BKF65-042, September 24, 1965