MARSBUGS:  The Electronic Exobiology Newsletter

Volume 2, Number 9, 22 June 1995.



Co-editors:



David Thomas, Life Sciences Department, Belleville Area College, 

Belleville, IL 62221, USA, thomasd@basenet.net (basegrp.com).



Julian Hiscox, Microbiology Department, BBRB 17, Room 361, 

University of Alabama at Birmingham, Birmingham, AL 35294-2170, 

USA, julian_hiscox@micro.microbio.uab.edu.



MARSBUGS is published on a weekly to quarterly basis as warranted 

by the number of articles and announcements.  Copyright exists 

with the co-editors, except for specific articles, in which 

instance copyright exists with the author/authors.  E-mail 

subscriptions are free, and may be obtained by contacting either 

of the editors.  Contributions are welcome, and should be 

submitted to either of the two editors.  Contributions should 

include a short biographical statement about the author(s) along 

with the author(s)' correspondence address.

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INDEX



1)	MARS PATHFINDER PASSES MAJOR SET OF ENGINEERING MILESTONES

	NASA press release.



2)	KEEPING A SATELLITE "EYE" ON ENVIRONMENTAL OFFENDERS

	ESA press release.



3)	MOVIE "CONGO" DRAWS ON SPACE RADAR STUDIES OF CENTRAL AFRICA

	NASA press release.

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MARS PATHFINDER PASSES MAJOR SET OF ENGINEERING MILESTONES

NASA press release.



Mars Pathfinder, a NASA Discovery program mission designed to 

deliver a lander, camera and instrument-laden rover to the 

Martian surface on July 4, 1997, has successfully completed an 

initial set of engineering tests intended to validate the 

spacecraft's unique atmospheric entry, descent and landing 

techniques.



"Mars Pathfinder will employ a new and innovative approach to 

placing a lander on the surface of Mars, in keeping with NASA's 

'faster, better and cheaper' philosophy of planetary 

exploration," said Tony Spear, Pathfinder project manager at 

NASA's Jet Propulsion Laboratory (JPL).



"This series of diverse tests has given us great confidence that 

the spacecraft will arrive safely and securely on Mars," Spear 

said.  "A truly exciting scientific mission will then be ready to 

unfold."



The Viking 1 and 2 Mars landers of the mid-1970s used a complex, 

computer-controlled liquid retrorocket system to achieve a soft 

landing at about five miles per hour (eight kilometers per hour).  

In contrast, the smaller, tetrahedral-shaped Pathfinder lander 

will use a combination of parachutes, solid-fuel rockets and 

inflatable air bags to perform a safe, relatively hard landing at 

about 35 miles per hour (56 kilometers per hour).



Recent parachute drop stability tests were performed by Pioneer 

Aerospace of Windsor, CT, in the desert near Yuma, AZ.  These 

tests successfully demonstrated the parachute configuration that 

will be used to bring the lander gracefully through the thin 

Martian atmosphere, said Ann Mauritz, JPL lead subsystem 

engineer.



Another element of the spacecraft's descent subsystems, the solid 

rocket motors, were tested at the China Lake Naval Weapons Center 

in Ridgecrest, CA. These tests involved dropping a simulated 

lander on a parachute from a helicopter and then firing three 

small prototype solid rockets to further slow the craft's fall 

toward the surface.



"The tests went just as predicted," said Dr. Les Compton, JPL 

lead subsystem engineer, with the simulated lander essentially 

coming to a dead stop in mid-air while at the same time 

maintaining a stable orientation with respect to the ground.  

Full-scale rocket prototypes, recently tested by Thiokol 

Corporation at Elkton, MD, will be used in full-scale subsystem 

tests to be carried out at China Lake later this summer.



Pathfinder's landing will be cushioned by four large air bags 

completely surrounding the lander's exterior petals. The air bag-

based soft landing was recently demonstrated by the air bag 

designers, ILC Dover of Frederica, DE, inside the 120-foot (36.5-

meter) vacuum chamber at the NASA Lewis Research Center's Plum 

Brook Station near Sandusky, OH.  The vacuum chamber provides a 

way to simulate the very thin atmosphere of Mars, and the tests 

demonstrated the viability of the air bag design in softening the 

force of the impact on the lander and its delicate payload.



The air bag was dropped from a height of 70 feet (21 meters) onto 

a 40-foot (12-meter) platform containing many large rocks similar 

to those found on Mars, according toTom Rivellini, JPL lead 

subsystem engineer.  "The initial full-scale prototype drop tests 

were very successful," Rivellini said.  "Engineers were able to 

test several air bag fabric construction techniques 

simultaneously.  The tests showed that air bags constructed of a 

double-layered fabric will be necessary to provide a sufficiently 

rugged cushioning effect." A second phase of prototype drop 

testing later this year will demonstrate the durability of the 

new double-layered air bags, at even higher impact levels.



Like Viking, the Pathfinder lander will arrive at Mars packaged 

inside a space capsule-shaped entry vehicle. Hitting the thin 

upper atmosphere of Mars at more than 17,000 miles per hour 

(27,000 kilometers per hour), the entry vehicle's heat shield 

will slow the craft to 900 miles per hour (1,450 kilometers per 

hour) in about two minutes. An onboard computer will sense the 

slow-down in speed and then deploy a large parachute. The 

parachute can slow the lander down to about 155 miles per hour 

(250 kilometers per hour) in the rarified atmosphere of Mars, 

which is only 1/100th as dense as Earth's.



An onboard radar altimeter inside the lander will monitor the 

distance to the ground.  At about 330 feet (100 meters) above the 

surface, the computer will inflate the air bags.



Seconds later, three solid rocket motors placed inside the top 

half of the entry vehicle above the lander will be fired.  In 

approximately two seconds, the rockets will bring the lander to a 

stop some 40 feet (12 meters) above the Martian ground. The 

parachute will be released, and the lander, nestled inside its 

protective air bag cocoon, will fall to the ground, bouncing and 

rolling until it stops.



Within about an hour, the air bags will be deflated and partially 

retracted toward the lander.  Pathfinder will then open its three 

metallic petals and stand itself right side up from any side that 

it happens to be lying on.  The microrover, attached to the 

inside of one of the petals, will be exposed to the Martian 

terrain for the first time. After the lander camera has taken a 

photograph of its position on the Martian surface, engineers will 

instruct the rover to drive off and begin exploring the immediate 

surroundings, an ancient Martian flood plain known as Ares 

Vallis.



Scheduled for launch in December 1996, Mars Pathfinder is part of 

a new generation of low-cost spacecraft with highly focused 

science goals designed to explore planets and other celestial 

bodies of the solar system.  Discovery missions are capped at 

$150 million (FY92) each in development costs and must be readied 

for launch within 36 months.



Mars Pathfinder is managed by the Jet Propulsion Laboratory for 

NASA's Office of Space Science, Washington, DC.

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KEEPING A SATELLITE "EYE" ON ENVIRONMENTAL OFFENDERS

ESA press release.



The Exxon Valdez disaster that occured on Good Friday in 1989 off 

the coast of Alaska is still a nightmare in the memories of many 

people.  The supertanker, about 330 metres long and carrying a 

cargo of over 200 000 tonnes of crude oil, was holed when it 

struck a reef.  Because of the time it took for the rescue 

services to arrive on the scene, over 40 000 tonnes of crude oil 

poured into the Prince William Sound, precipitating an 

environmental catastrosphe of unimaginable proportions.  A 

stretch of coastline over 1500 kilometres in length was covered 

by a thick layer of oil and an estimated 400 000 sea birds died 

from oil pollution, not to mention the effects on marine life -- 

fish chocked because their gills were glued with oil, light was 

obscured destroying large expanses of algae and swarms of 

planktons perished because the oil lying on the sea surface 

prevented an exchange of gases with the atmosphere.



But the Exxon Valdez accident was not the first of such tanker 

disasters and by no means the worst to have afflicted the Earth's 

oceans.  Eleven years earlier, in March 1978, the Amoco Cadiz, a 

Liberian-registered tanker, ran aground off the French port of 

Brest and broke up.  Its entire cargo of 230 000 tonnes of crude 

oil poured into the sea.  In July 1979, two supertankers, the 

Atlantic Empress and the Aegean Captain collided off the coast of 

Tobago.  The Atlantic Empress was carrying 276 000 tonnes of 

crude oil and sank two weeks later.



Every supertanker accident generating large-scale pollution makes 

the headlines.  But is is not only spectacular cases such as 

these that pose a threat to the environment.  The numerous small 

oil slicks that poison the high seas when ships' captains flush 

out their tanks at dead of night are equally to blame.  At the 

end of the 1980s, the American National Research Council 

estimated that this practice accounted for a yearly average of 

over 3 million tonnes of oil in the world's ocean -- enough to 

fill twenty tankers the size of the Exxon Valdez.  Accidents on 

drilling platforms and leaks in pipelines linking offshore oil 

rigs with the mainland also give cause for great concern since, 

in addition to environmental damage, which is hard to estimate, 

they represent a tangible financial loss.



For as long as pipelines are inspected in only a few, closely 

delimited and mostly coastal zones, it will be impossible to 

monitor the seas using conventional means for the purpose of 

identifying environmental offenders because of the mainly 

financial but also the meteorological obstacles standing in the 

way.  In any event about 70% of the Earth's surface consists of 

oceans and it is impossible to provide uninterrupted satellite 

surveillance of the whole area.  Even from space, it is very 

difficult to identify offenders or detect pipeline leaks using 

conventional Earth observation methods because in daytime fog, 

clouds and reflected sunlight greatly hinder the detection of oil 

slicks and in the dark all cats are grey.  Similar limitations 

prevent swift appraisal of the threat posed by tanker accidents 

although this is necessary in order to take rescue measures and 

coordinate them.  For some years now, a solution to this dilemma 

has been available.  It lies in the use of satellite radar 

instruments including those on board the European remote-sensing 

satellite, ERS-1, which has been circling the Earth since summer 

1991.  These instruments can detect even quite small oil slicks 

from space.  This is possible because of the "smoothing" effect 

of oil on waves.



As Professor Olaf M. Johannessen of the Nansen Environmental and 

Remote-Sensing Centre at Solheimsviken (Norway) explains: 

"Satellites with active microwave sensors illuminate the scene to 

be observed and record the amplitude as well as the "phase" of 

the backscattered radar signal.  The return signal depends among 

other things on the sea surface roughness, which, at a first 

approximation, is described by short Bragg waves (at centimetre 

wavelengths).  Because oil dampens the Bragg waves, oil spills 

show up in the radar images as dark areas while the sea around 

them is bright.  However, there are other phenomena that dampen 

the Bragg waves too, such as thin layers of algae, which produce 

a similar radar image."



The ERS-1 environmental research satellite, which belongs to the 

European Space Agency (ESA), is one of the first satellites to be 

equipped with an active radar system of this type.  Using a very 

special radar antenna, it takes high spatial-resolution 

"pictures" of the Earth's surface.  Since the resolution or 

acuity of vision of a detector depends primarily on the antenna 

diameter, the system used is described as the synthetic aperture 

radar (SAR).  It exploits the fact that the satellite moves a 

little further along its orbit between the time of emission of 

the radar beam and reception of the return signal.  The resulting 

succession of backscatter signals shows the same swath of the 

Earth's surface from slightly staggered angles of vision.  Once 

they have been analysed by computer and simultaneously 

superimposed, reception with a considerably larger antenna can be 

simulated, thereby producing an artificial increase in aperture 

size.  This gives the ERS-1 antenna, measuring ten metres in 

length, the same resolution as an antenna with an 800-metre 

diameter and in "image mode" it produces radar pictures of the 

surface of the Earth or its oceans with a pixel size 

corresponding to an area of only 30 m x 30 m.



However, the SAR cannot clearly identify an oil slick in every 

case.  Even a clean sea surface shows up as a dark patch on a SAR 

image when wind speed does not exceed 3 m/s (corresponding to a 

wind force of about 2).  In such cases, sea surface roughness 

caused by what is only light breeze is not sufficient to produce 

a discernable impact on the backscatter from the radar beam.  On 

the other hand, the smoothing effect of at least thin oil slicks 

at wind speed above 10 m/s (corresponding to a wind force of 6) 

is not sufficient to produce a recognisable difference in surface 

roughness and consequently in sea surface backscatter response.



During the ERS trial phase, 20 tonnes of crude oil were poured 

under supervision into the sea in the Haltenbanken region of 

Norway in order to demonstrate how oil spills are detected, 

acquire experience and take calibration measurements.  The oil 

slick was then removed.  The results of this operation have since 

proved valuable for detecting and pinpointing countless incidents 

of oil pollution in the Earth's oceans.



One of ERS-1's most impressive achievement was its demonstration 

of the superiority of radar observation from space in December 

1992 when the Aegean Sea tanker ran aground off the port of La 

Coruna in northwest Spain, broke up and finally exploded, 

emptying its entire cargo of about 79 000 tonnes of crude oil 

into the sea.



It was not until ten days later, when ERS-1 flew over the scene 

for the first time and observed it using its SAR instrument, that 

the extant of the oil slick became clearly apparent.  Blown by 

southerly and westerly winds, the oil had already spread over an 

area several hundred metres square and in addition had penetrated 

the bay east of La Coruna.  In all, a stretch of more than 200 

kilometres of coastline was polluted.  In mid- December the wind 

veered southeast to northeast, driving the slick westwards along 

the coast to the islands of Sisargas.



The next time ERS-1 passed over the area, early in January 1993, 

the SAR image showed the slick to be breaking up further off the 

coast and on 17 January, the whole area appeared to be 

"clean"again.  But high waves must have prevented the detection 

of oil residues because on 8 February, when the sea was calm, 

remnants with long "trails" were clearly visible, particularly in 

areas adjoining several bays.



Dr. J. Lichtenegger, who works at ESA's data-processing centre 

ESRIN (Frascati, Italy) makes the following comment: "The ERS-1 

observations over this period showed that SAR data can be a 

valuable tool for the detection and monitoring of oil slicks, not 

only because they can be gathered regardless of cloud cover but 

also, and above all, because they can be made available so 

quickly." The mass of data produced by SAR is enormous -- up to 

120 megabits a second (equivalent to 5600 pages of text).  As the 

data cannot be stored on board the satellite, they have to be 

transmitted in real time to a ground station in the satellite's 

direct line of sight.  For this purpose, ESA operates four ERS 

stations in Europe and Canada, which are supplemented by twenty 

or so national stations spread across the world.  The "express 

processing" of raw data to produce usable numerical data and 

images means that only a few hours after reception at the Kiruna 

(Sweden) or Fucino (Italy) station, the relevant information can 

be passed on to users in Europe and elsewhere.



However, notwithstanding spectacular tanker accidents, which 

never fail to capture the attention of the media, a much bigger 

cause of ocean pollution is the deliberate policy of secretly 

tipping oil residues into the sea.  This urgently calls for 

monitoring of the high seas, which cannot be done as part of the 

routine inspections carried out by national coastguard partols.  

Here too, trial observations using ERS-1 have shown that, in the 

Mediterranean for instance, such illegal practices can swiftly be 

detected and the offenders identified beyond all doubt provided 

satellite overpass follow in quick enough succession.



When the satellite passes over the Earth's extreme northern and 

southern areas, this time requirement is in any event guaranteed.  

Since the ERS-1's orbit lies, more or less over the poles, there 

is a big overlap of the areas covered on each overpass, with the 

result that the satellite can collect data more frequently than 

it can in an area close to the equator.  For some years, Norway 

has been taking advantage of this orbit and using ERS data to 

monitor its coastal zones.  Furthermore, it has set up its own 

receiving station in Tromso which is jointly operated by the SFT 

-- the Norwegian environmental monitoring office -- some oil 

companies and a firm specialising in oil-pollution control, and 

is supplied with ERS-1 data by ESA.  Data are recorded and pre-

processed before being forwarded to a data-processing centre for 

which Norwegian defence ministry is responsible.  From there they 

are sent directly to the environmental monitoring office.  Other 

countries want to follow suit and the Netherlands has already 

completed a successful pilot phase.

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MOVIE "CONGO" DRAWS ON SPACE RADAR STUDIES OF CENTRAL AFRICA

NASA press release.



"Congo," the most popular movie in America this week, depicts 

futuristic remote-sensing technology and satellite communication.



In real-life, scientists at NASA's Jet Propulsion Laboratory have 

used imaging radar flying aboard the space shuttle to study the 

habitat of the mountain gorillas of Central Africa -- the same 

area where "Congo" takes place.



"The Virunga volcano chain in Rwanda, the area that's also 

depicted in the film, is ideally suited for study by radar 

because the mountains are perennially covered by clouds and the 

radar is able to see through clouds," said Dr. Diane Evans, the 

radar project scientist at JPL.



The data were taken by the Spaceborne Imaging Radar C/X-band 

Synthetic Aperture Radar (SIR-C/X-SAR), part of NASA's Space 

Radar Laboratory which flew onboard the space shuttle Endeavour 

in April and October 1994.



"We had actually targeted this area for study because it's also 

an active volcano area -- another point which is made in the 

movie -- and we are involved in studying several volcanoes around 

the world that are potential threats to the local populations," 

Evans said.



Evans and her team have provided the radar data to scientists at 

the Dian Fossey Gorilla Fund in London and Rutgers University in 

New Jersey. Those researchers have constructed a map of the 

gorilla habitat using the JPL radar data and provided the map to 

the producers of "Congo" for use in the movie.



"When the book 'Congo' was written in the early 1980s, the 

technology seemed very futuristic, but here we are in 1995 and 

this technology has become a reality," Evans said.



The study of the gorilla habitat is just one of several 

experiments conducted by SIR-C/X-SAR.  Scientists are continuing 

to analyze data from several hundred sites around the globe which 

they hope will aid them in their studies of Earth's changing 

environment.



SIR-C/X-SAR is a joint mission of NASA and the German and Italian 

space agencies.  JPL manages the SIR-C portion of the mission for 

NASA's Office of Mission to Planet Earth.

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