|Reentry Series: Implementation Roadmap|
Engineering Synthetic Meteor Showers
In developing an understanding of the technology required to execute these artworks, inquiries have been made and discussions conducted with scientists in Meteor Astronomy and related fields. What has emerged from these discussions is the realization that the execution of these artworks provides opportunities for conducting parallel science. This is obviously a unique position for an artwork to occupy.
The creation of synthetic meteors involves a sufficiently rarefied corner of the physical world so as to encounter
limits to the current scientific knowledge of the mechanisms involved. However, it transpires that these mechanisms may in fact be
critical to the development of life on earth. Meteors have been postulated as one possible delivery mechanism for the primordial
carbon compounds required for the development of life, compounds which do not occur naturally within the planetary formation process
which created the earth. These compounds exist instead in deep space, and were required to have been transported somehow to the
surface of the early earth. Understanding these delivery mechanisms is fundamental to developing an understanding of the formation
of life on this and other planets.
European Space Agency Ariane 5 booster
a Reentry Series launch candidate
In establishing a working relationship with these scientists an informal compact between art and science has been made. It is agreed that funding for the execution of a piece would be obtained under the guise of the artwork itself, so costs such as the fabrication of the sacrificial payloads, deployment vehicle, and launch would be borne by the artwork funding. Any scientific study would be independently funded by a purely scientific grant. Such studies might deal with accurately measuring the light output of a synthetic meteor of know mass, composition, and velocity, a rare opportunity. Only one such study has ever been conducted, by researchers from NASA and MIT in 1963 (1). Another area of interest is measuring the temperature of the meteor and its wake, to determine if the primordial carbon compounds could survive the reentry process. Other areas of study involve measuring the rate of ablation of the meteors using highly accurate radar to verify reentry heating models.
With this attendant scrutiny of the artwork by scientists and their essential input on the technical requirements of the piece, it becomes a truly interdisciplinary work. This becomes fully evident when the possibility is considered of the artworks being subtly modified to accommodate the interests of the scientists. For instance, if a number of materials are available for synthetic meteor composition, all with essentially the same visual properties but some being of greater interest to the scientific community, it would be logical to accommodate the interests of the scientists. However, it has been established that the artworks have primacy due to their being funded independently. No decisions would be made which would compromise the integrity of the artworks in the interests of making better science. However, there is a broad field for potential compromise on a host of issues, some major, some minor. The first major such issue is that of the velocity of the synthetic meteors. This is discussed in detail below. This may involve an interesting trade-off between the fidelity of the synthetic meteors to naturally occurring ones and the economics of creating such an artwork.
From a technological standpoint the following is the development cycle required to be able to routinely execute Reentry Pieces.
ODERACS Deployment, Space Shuttle Cargo Bay
A delivery mechanism for synthetic meteors?
The fundamental questions surrounding the design of a synthetic meteor involve the mass, velocity, mechanical structure, and chemical composition required to achieve a desired brightness sufficient for observation under a given viewing condition, such as the night lights of a city. The mass requirements are a critical parameter as they drive launch cost and deployment vehicle design. Preliminary estimates were as high as hundreds of kilograms of mass per synthetic meteorite. Recent data from the NASA Orbital Debris Program Office and noted meteor astronomer Dr. Peter Jennniskens have resulted in a significant downward revision of the estimated mass.
The factors of velocity and composition are interrelated with mass in determining brightness. For instance, it is believed that brightness is a function of the square of velocity, in which case it might prove more efficient to accelerate a smaller mass to a higher velocity. Similarly, brightness is a function of composition, using a more massive material which produces a brighter meteor might prove more efficient. In addition, the mechanical structure of the meteoroid is extremely important in insuring desired luminosity characteristics over time. For example, a solid object might require an excessive period of time to heat sufficiently to begin the vaporization which is required for luminous onset, making a less dense, lattice like structure preferable to a solid. To some degree these relationships are unknown or at the forefront of current meteor research, creating the requirement for at least some flight testing of synthetic meteoroids.
Establishing Mass Limits
In an attempt to begin to establish useful ranges for the parameters it was decided to make complete meteoroid reentry demise the determinant
for maximum payload mass.
The primary objective of the program must be safety for those on the ground. Under no conditions could a payload survive reentry and reach
the earth's surface.
The NASA Orbital Debris Program Office generously agreed to model various payload masses using their reentry demise modeling
software to determine an approximate upper limit for payload mass which would still assure complete reentry burnup. Solid iron spheres
were modeled for
a variety of reasons. A spherical shape does not require orientation of the payload with respect to its flightpath, simplifying the
deployment vehicle. Iron was chosen as a material since many meteorites are primarily composed of iron and this would hopefully provide
similar brightness performance by the sacrificial payloads. The Orbital Debris Office performed data runs for .1, 1, 10, and 100 kg. masses.
They found that for a zero
degree or flat flight path angle, as if reentering from low earth orbit at 78 km at a speed of 8 km/s, .1 and 1 kg solid iron spheres will
completely demise before reaching
the earth, in times of 88 and 148 seconds respectively. At time of demise they would still be traveling at 6 km/s.
The 10 and 100 kg spheres would reach the earth's surface. Solid iron spheres
have a diameter of 6.24 cm for a 1 kg sphere and 2.9 cm for a .1 kg sphere, so these are not large objects, effectively pinball to
baseball sized assuming a solid structure.
Pegasus Air-Launched Orbital System
another Reentry Series launch candidate
Laboratory for Atmospheric and Space Physics
Univeristy of Colorado, Boulder
So, a .1 to 1 kg mass, reentering at meteor velocities would be sufficiently bright. The next question is will this observed behavior on the part of meteors extend to the lower velocities resulting from decay of Low Earth Orbit. The answer is probably yes. The Orbital Debris data indicates the mass will demise, so it will be vaporized and become luminescent. The lower velocity will result in reduced visibility as meteor luminosity is known to be proportional to the square of velocity. This would mean that a meteoroid traveling at 8 km/s would produce only 16% of the instantaneous brightness of one moving at 20km/s. However, the loss in apparent luminosity may not be as great, as the object is slower moving. The integral of the luminosity per subtended viewing angle would be reduced to only 40% of the faster moving meteor and this may be a better measure of the relative apparent brightness.
The Velocity Question
Convergence on a optimal synthetic meteor design solution will require study and recommendations by leading meteor researchers. The issue of reentry velocity has emerged as a major unknown. Preliminary discussions have suggested that the most cost-effective launch technology for payloads in the 10s of kilograms range (nominally 10 synthetic meteoroids and a deployment vehicle) would be to piggy-back on a low earth orbit launch dedicated primarily to another function, such as International Space Station resupply or commercial satellite launch. The reentry velocities available from such a launch profile would be in the 7 to 8 km/s range. Reasonable brightness characteristics would be available from reentry velocities in this range.
However, these LEO reentry velocities are not sufficient to guarantee fidelity to naturally occurring meteors, an issue for some of the parallel science contemplated in association with the mounting of these works. Dr. Jenniskens has indicated that he would like to see a minimum reentry velocity of 15 km/s for certain experiments he would like to perform. The potential problem is that attaining these higher velocities is expensive from an energy expenditure perspective and almost certainly would require a dedicated launch, both factors potentially driving costs higher. On the other hand, these higher velocities would produce brighter meteors by a factor of as much as 4 or reduce the mass requirements for a given visibility by a factor of 4. This is an interesting cost/benefit tradeoff and will be a focus of much of the work in resolving the design of the synthetic meteoroids.
2. Document Similar Reentry Events to Assess Visual Attributes and Experience
Since atmospheric reentry of space vehicles or large fireball size meteors are such infrequent events, few people have had direct encounters with these
phenomena. In an effort to better appreciate and convey the visual experience of these events to potential benefactors as well as host cities
it is desirable to provide a record of reentry events with similar characteristics to the synthetic meteor artworks. If such similar events
could be identified, still and video imagery would be recorded, with backgrounds giving an idea of scale and relative brightness when ever
The Stardust Luanch, 1999 and a sample
return capsule after a desert drop test
A very interesting potential for documenting a similar reentry event was suggested by Dr. Jenniskens. He is studying reentering man-made objects for the same reasons as he has expressed interest in studying the Reentry Pieces. A exceptional event of this type is to occur early in 2006 with the return of the Stardust SRC or Sample Return Capsule. Stardust is a mission launched in 1999 which involves the sample and return of cometary matter and interstellar dust, the first return of extraterrestrial material from beyond the moon's orbit. The vehicle made a near pass of comet Wild 2 in January 2004 collecting material and will reenter the earth's atmosphere at 3:00 AM, January 15th 2006, over Utah. The vehicle will mark the fastest vehicle reentry since the Apollo program, of nearly 13 km/s, approaching meteoric velocities. The capsule is only .8 meters in diameter and the expected visual magnitude is -7.8, right in the range of the Reentry Piece synthetic meteors. Dr Jenniskens is studying the event to "probe the delivery of organics for life's origin by measuring the physical conditions during reentry."
At a minimum the artist will mount a concerted effort to obtain as much documentary material as possible of this event as it will mark
the only foreseeable opportunity to study an event of such similarity to an individual synthetic meteor in the Reentry Series. The Heaven & Earth
Foundation will attempt to obtain grant funding to provide a more in-depth documentation of the event than the artist is able using his own resources.
An attempt will also be made to coordinate with Dr. Jennisken's Stardust SRC Observing Campaign
to provide and exchange documentary data.
3. Select Launch System
A Japanese TR-IA Sounding Rocket
Japan Aerospace Exploration Agency Photo
Ballistic launches, on the other hand, provide an entirely different set of capabilities. While orbital system reentry paths are restricted to relatively flat flight path angles, essentially parallel to the horizon, ballistic systems could provide very steep flight path angles right up to normal to the earth's surface, or straight down. Ballistic launches also provide the ability to achieve higher reentry velocities. Orbital Sciences Corporation, of Dulles Virginia, USA, have indicated that they may have the capability to achieve reentry velocities as high as 30 km/s in a program designed to test heat shields for the manned Mars mission. A variety of boosters are available for ballistic missions including de-comissioned ICBMs such as the Peacekeeper or Minotaur down to so-called sounding rockets, used for meteorological sampling. A ballistic mission would almost certainly require a dedicated launch, however the lower cost of sounding rockets and potentially simpler deployment vehicle might prove cost-competitive with an orbital launch. This is due to the fact that an orbital system might require a deployment vehicle thruster to provide a de-orbit burn.
The choice of a launch system is critical and is ultimately highly inter-related with the design of the synthetic meteoroids themselves.
4. Design and Construct Deployment System
ODERACS Sphere Delivery System
It has been suggested that the academic community be involved for participation in the design and construction of the deployment
vehicle. Graduate programs in aerospace engineering are eager for the rare opportunity to design and construct hardware which will actually
be deployed in space and can provide a very cost-effective alternative to commercial aerospace firms.
This approach has been used successfully by the NASA Orbital Debris Program Office to develop the deployment
vehicle or "sphere delivery system" for the ODERACS project, probably the device most closely resembling the synthetic meteoroid
deployment system found thus far. ODERACS, for Orbital DEbris RAdar Calibration Spheres, was a mission flown as a Space Shuttle "Getaway
Special" in 1994 to release metallic spheres of a known diameter to accurately calibrate the ground based radars which track orbital debris.
5. Flight Test Payload
A Progress Vehicle atop a Soyuz Booster
gantry at Baikonur Cosmodrome, Khazakstan
S.P. Korolev Rocket and Space Corporation Photo
A development scenario has been proposed for relatively low-cost and timely flight testing. The International Space Station is
routinely re-supplied by Russian Soyuz/Progress robotic vehicles, produced by the S.P.Korolev Rocket and Space Corporation Energia,
which deliver two and a half tons of supplies to the station every few
months. The vehicles blast off from the massive Baikonur Cosmodrome in Kazakhstan and reenter and burn up in the atmosphere after having been loaded with refuse from the station. It would appear that the
Russians are allowing modest piggy-back missions to be flown on Progress flights. It has been suggested to approach the Russian
launch program managers via European Space Agency intermediaries about flying a synthetic
meteor test as a Progress re-supply piggy-back.
After the Progress vehicles have resupplied the Station they are guided to a planned reentry demise over the South Pacific. Prior to the demise
the piggy-back mission would be activated, releasing one or more test synthetic meteoroids. The guidance and de-orbit thruster capabilities
of the Progress vehicle would be employed for the piggy-back mission, reducing the deployment system requirement to a simple mechanical
release system, similar to ODERACS. The deployment over isolated regions is compatible with the test objectives of safely verifying
performance, but does somewhat complicate the performance validation aspects.
The artist is in the process of investigating this possible test scenario.
6. Debut Reentry Piece
Studies for Synthetic Meteors V1.0
frame from video animation
The potential for a Reentry Piece to alarm the population on the ground is another possible concern for any host city and the relatively small and contained population of the Hawaiian Islands would provide a controlled opportunity to address these concerns. The total population of the islands is only about 1.2 million with nearly 75 percent of that population being in Honolulu City and County. A concerted effort would be made to publicize the event in advance, and then an assessment could then be readily made of any significant increase in 911 or emergency services calls. Unlike the situation on the mainland, where the event might be seen by residents of localities relatively far removed from the host city or recent visitors who are not aware of the artwork, the Island's character allows a more uniform level of notification.
The above describe the major signposts on the roadmap for ultimate realization of the Reentry Pieces. The Heaven & Earth Foundation will be applying for study grants to allow all parties to begin to address some of the uncertainties as well as develop budgetary requirements and cost analyses of the various trade-offs. Once these analyses are complete basic decisions on candidate technologies can be made and grants for full funding of the first artwork applied for.
1) Results from an Artificial Iron Meteoriod at 10 km/sec, R. E. McCrosky and R. K. Soberman, Smithsonian Contributions to Astrophysics, Vol 7, 1963