Many space professionals are looking forward to further space exploration using electric thrusters (ET). Unlike ordinary chemical propulsion systems, ET demonstrate much more higher exhaust velocity, since the propellant is accelerated for propulsion by electric power being supplied from an onboard source. The thrust produced by ET is very small - not more then a few grams so that ET cannot burst a rocket from the Earth surface. ET can tick only on board any orbiting satellite or spaceship.
The high exhaust velocity distinguished by ET offers noticeable propellant saving for given maneuver in space as compared to chemical propulsion so that mass reduction of a communication satellite for instance may be up to a few hundreds kilos. As a result this more lightweight satellite could be lifted in orbit by less heavy launch vehicle saving millions of dollars.
However money saving is not the only profit. A less heavy rocket is less hazardous for environment. ET themselves are ecologically pure using as non-detrimental propellants as noble gases, hydrogen, ammonia.
The benefit of electric propulsion will be more fully realized when significant cargo traffic arises in space providing deployment of large space structures, colonization of the Moon and planet exploration. That is why ET are included in such ambitious projects currently under development as Electric Orbit Transfer Vehicle, Lunar Ferry and some unmanned mission to planet. Over these projects the flight use of ET would save hundreds millions of dollars with better ecology.
Currently we are present at the beginning of the "gold century" of electric propulsion. To make it reality the electric propulsion community in many countries is going on with research and development of ET of different types either for secondary on-orbit application or for primary propulsion of multikilowatt level.
However what is a place of radio amateurs in the matter - an impatient reader could ask. Do not be in a hurry, dear reader, do not put reading this article off and you in a few minutes realize that the VHF-community could play its role in ET implementation if wants.
Integration of ET with onboard equipment poses a certain set of problems to be solved such as electromagnetic compatibility of ET. Particularly the matter is that highly ionized exhaust plumes of ET may scatter RF-signals producing large "dead" zone for communications.
This plasma screening effect should be thoroughly studied before electric thrusters become standard onboard equipment. The investigation will help designers of future electrically propelled spacecrafts to minimize the hazard of communication disruption by ET plasma plumes.
In 1987 specialists of Central Research Institute of Machine Building (TSNIIMASH) conducted a series of space plasma experiments in order to evaluate the shape of mentioned above "dead" zone using KOSMOS satellites with onboard arcjet plasma source.
The well known method of radio sounding was used for plasma monitoring. The telemetric and command signals emitted by onboard antennas played a role of sounding signals. Passed through plasma these signals were simultaneously received by a number of on-ground measuring sites. The shadow effect was clearly observed however the precise data on the shadow boundary shape and its dynamics could not be obtained in the experiments of 1987 since the receiving network was too rarefied. Deployment of properly dense special receiving network is extremely expensive and consequently unrealistic.
Possible solution is to use available worldwide spread network of amateur VHF receivers. This idea was put in the base of an proposal to perform a new plasma space experiment on the International Space Station (ISS) almost in the same layout as in 1987.
Methodologically SpEx "Shadow" is oriented to using of amateur packet radio and Internet technology and resources.
The objectives of the work is observation and evaluation of refraction/scattering effects in artificial plasmas using method of RF sounding in space experiments under different geophysical conditions.
Fig.1. SpEx "Shadow" lay out
SpEx "Shadow" lay out is shown in Fig.1. In the chosen region the onboard arcjet source injects a plasma plume in space and the onboard radio beacon transmits VHF sounding signals in the form of the Universal Time marks. Passed through the plasma these signals are being instantly received by an on-ground measuring VHF network. Due to refraction/scattering of the sounding signals in the exhaust plume, the shadow region would arise adjacent to the satellite. When the shadow boundary running after the satellite along the Earth surface reaches any on-ground receiving site the signal cut-off is to be registered. The task of every individual participant is to register moments of signal cut-off and following signal restore using the Universal Time marks and to address this information along with data on its geographical position to the Information Storing Center. Every operation sequence would take 6-8 min. while the satellite is passing between two opposite points of the local radio horizon. It is interesting to perform the experiment in different geophysical conditions.
The amateur packet radio technology in the SpEx "Shadow" as proposed by astronaut Alexander Kalery, offers the possibility to use Internet transport resources either for net-work notification or for data collection. Principally the available receiving network may be provided with Universal Time Marks if the onboard radio beacon merely transmits packets of minimal duration in format of AX25 Protocol.
This promises to perform large-scale monitoring of an artificial plasma nonhomogeneity using the mosaics of on-ground receiving sites.
The same technology can be also applied in space experiment on sounding of not artificially injected plasma, but of the natural ionospheric plasma in HF frequency band (14 MHz). It is expected, that due to dispersion of sounding radiation in ionospheric plasma, an "irradiated" spot should appear on the Earth surface, and determination of boundaries of this "irradiated" spot is the purpose of space experiment (legend "Spot"), which can be carried out not necessarily on the ISS.
The scientific results the SpEx "Shadow" will help designers of future electrically propelled spacecrafts to minimize the hazard of communication disruption by ET plasma plumes.
Except the scientific issues, realization of the space experiment "Shadow" will give an unique experience in involving of intellectual and technical potential of International radio amateur community as well as Internet technology and resources for monitoring of the near-Earth space and to evaluate capability to use this potential in perspective scientific projects.
Actually the space experiment "Shadow" is an interesting attempt to use Internet for principally new goal - not only for information spreading but also as an effective measuring tool in spatially large-scale scientific researches.
The space experiment "Shadow" may also bring an important social result attracting public attention to advanced technology, astronautics, amateur packet radio and Internet.
With really mass, voluntary and gratuitous participation of VHF-amateurs this project would become a humanitarian world wide action uniting many peoples of different countries with interesting and useful work for future enhancing the spirit of cooperation, mutual understanding and friendship.
As it was mentioned above the space experiment "Shadow" may be successfully performed under the condition that the number of participants will be great enough . The greater this number the more precise scientific result would be issued.
As claims for participation in the SpEx "Shadow" appear at the Information Storing Center in response to this initial invitation, we are going to select perspective "measuring fields" where the receiving network is dense enough and where the bulk of activity will be further concentrated.
The SpEx "Shadow" will be performed in two stages:
• of "cold" (with no plasma injection) planned over February - June 2011 as a SpEx "Shadow-beacon" (beacon for shadow) and
• of full scale "hot" (with plasma injection) experiments.
After successful fulfillment of the "cold" phase it will be possible to accept the justified solution on realization of a series of full scale "hot" experiments later.
If you do not mind to take part in the experiment, do as follows:
1) Visit www.tsniimash.ru, page SpEx "Shadow-beacon", make registration and subscription for news;
2) e-mail your decision to the Information Storing Center firstname.lastname@example.org or email@example.com with short personnel data: name, call sign, QTH, available radio equipment, your wish on experiment run conditions (day or night time, week-end and so on);
3) Look through the available results of observation;
4) Permanently look through current news;
5) Take part in experiment runs and e-mail your report (log-file) to the Information Storing Center;
Every participant of the space experiment "Shadow-beacon" will be awarded with special certificate.
SpEx "Shadow-beacon" program supervisor – Oleg Alifanov, Dean of Moscow Aviation Institute.
Principal investigator - project author Valentin Strashinski (TSNIIMASH).
Onboard beacon operators – from ISS crew.
On-ground receiving network operators - YOU!