The Mars Exploration Rovers Spirit and Opportunity landed on Mars on January 4, 2004 and January 25, 2004, respectively. Spirit continued operating until contact was lost on March 22, 2010, a total of 2,269 Earth days, which is 2,208 days on Mars (sols)1. Spirit operated on the Martian surface 24.5 times as long as its design life of 90 sols.
Even more amazing: Opportunity has been operating on the Martian surface (as of this publication date) for 5,108 Earth days, which is 4,971 sols. That’s 55.2 times its design life of 90 sols!
Spirit and Opportunity faced their greatest challenge up to that point during the global Martian dust storm of July 2007. Here is what I wrote about it back then.
Spirit and Opportunity‘s Greatest Challenge (7-26-07)
The intrepid Mars Exploration Rovers Spirit and Opportunity—which have been operating on the surface of Mars over 14 times longer than planned—each carry two 8 amp-hour lithium batteries, and these batteries are charged by solar panels. Before dust storms began significantly reducing the amount of sunlight reaching the rovers’ solar panels, they were generating about 700 watt-hours of electricity each day—enough to power a 100-watt light bulb for seven hours. Not much, it may seem, but plenty enough to operate each rover’s internal heaters, motors, scientific instruments, and communication equipment.
In recent weeks, both rovers have seriously been affected by the dust storms, particularly Opportunity which last week was able to generate only 128 watt-hours of electricity on the worst day. With precious little energy to replenish the internal batteries, controllers have hunkered down the rovers to conserve energy for the most critical need—internal heaters to keep the core electronics warm enough to operate. Remember, the average surface temperature on Mars is -85° F!
At press time, weather conditions appear to be improving for both rovers, but there are still worries that the rovers could have been damaged by all that dust blowing at them for days on end.
As it turns out, after the global dust storm of 2007 subsided, the rovers benefited from subsequent “cleaning events” where the winds of Mars blew most of the dust off of the solar panels.
There have been no global dust storms on Mars since 2007; however, another one is anticipated later this year. Hopefully, our intrepid Opportunity will weather the storm and continue to generate enough life-giving power from its precious solar panels .
1A Martian day is called a sol and is slightly longer than an Earth day. A mean solar day on Earth is 24h00m00s, by definition, but a mean solar day on Mars is 24h39m35.244s Earth time. To convert Earth days to Martian sols, divide the number of Earth days by 1.0275.
While video recording the star Tycho 1311-1818-1 in Taurus on a very cold Thursday evening last week (-4° F) in the hope that asteroid 126561 (2002 CF105) would pass in front of it (it didn’t), I was surprised and delighted to serendipitously record a very slow moving Earth-orbiting satellite crossing the field. Now, in order to see a satellite, it must be illuminated by sunlight. But to see any satellite during the first week of January only 10 minutes before local midnight, it must be very far from the Earth indeed (more on that later).
Here’s a video of the event showing its complete traversal of the field of view:
I’m hoping that one of the good people that frequent the satellite observers’ forum SeeSat-L will be able to identify this unusual object. Requisite to that, of course, are two precise positions at two precise times and the observer’s location.
A very useful online tool provided by the Department of Physics at Virginia Tech allows one to input the right ascension, declination, and x-y coordinates of between 4 and 10 known objects, and it does an astrometric solution across the field so you can determine the right ascension and declination of an unknown object.
At 5 Jan 2018 5:42:58.122 UT, the satellite was located at:
5h45m48.14s +21°45’17.5″ (apparent coordinates, epoch of date).
At 5 Jan 2018 5:50:22.931 UT, the satellite was located at:
5h46m53.98s +21°48’06.3″ (apparent coordinates, epoch of date).
Observer Location: 42°57’36.9″N, 90°08’31.1″ W, 390 m.
Using the satellite coordinates above, and the angular separationcalculator kindly provided by the Indian Institute of Astrophysics, we find that the satellite traversed just 0.2590° in 0.1236 hours. That’s 2.095° per hour, or only about four moon diameters in an hour!
Surely, this satellite must be way out there. How far? To determine that, I did a couple of what we used to call during my college physics days “back-of-the-envelope” (BOTEC) calculations. These are rough approximations—using simplifying assumptions—that should get you to an answer that is at least the right order of magnitude.
If we can estimate the orbital angular velocity of the satellite, we can determine its orbital period, and if we could determine that, we can calculate it orbital distance. Now, we don’t know yet if this satellite is in a near-circular or highly-elliptical orbit. If the satellite is an a highly-elliptical orbit and we observe it near apogee, its angular velocity will be somewhat slower than the angular velocity of a circular orbit at that same distance. If we observe it near perigee, then its angular velocity will be somewhat faster that the angular velocity of a circular orbit at that same distance. First simplifying assumption: let’s assume a circular orbit.
The next simplifying assumptions are that (1) the satellite passes through the observer’s zenith, and (2) the distance to the satellite is large in comparison to the radius of the Earth. At the time of observation, the satellite was at an altitude between 65° and 66° above the horizon. Not quite the zenith, but maybe close enough.
First, we need to compensate for the fact that the observer’s location on the surface of the Earth is moving in the same direction (along right ascension) as the satellite is orbiting (eastward) as the Earth rotates. We need to add the Earth’s rotational velocity to the right ascension component of the satellite’s velocity to get its true angular velocity relative to the center of the Earth. This of course assumes that the radius of the Earth is small compared to the distance to the satellite.
During the 0.1236 hours we observed the satellite, it moved 0.2743° eastward in right ascension and 0.0469° northward in declination. We now need to add a portion of the Earth’s angular velocity to the right ascension component of the satellite’s angular velocity. If the satellite were at the north celestial pole, the amount we would add would be zero. If, on the other hand, the satellite were on the celestial equator, we would add the full amount. Since cos 90° is 0 and cos 0° is 1, let’s add the Earth’s rotational angular velocity times the cosine of the satellite’s declination to the right ascension component of the satellite’s angular velocity.
The Earth turns through 360° in one mean sidereal day (23h 56m 04s = 86,164s). That’s 1.8591° during the 0.1236 hours we observed the satellite. Taking that times the average declination of the satellite during the observation time, we get 1.8591° cos 21.7783° =1.7264°. Adding this to the 0.2743° the satellite moved in right ascension, we get new components for the satellite’s angular displacement of 0.2743° + 1.7264° = 2.0007° in right ascension and 0.0469° in declination. This gives us the “true” angular displacement for the satellite of
This is a motion of about 16.19° per hour, giving us a rough orbital period of 22.235 hours or 80,045 seconds.
Using Newton’s form of Kepler’s Third Law to calculate the orbital semi-major axis, we get (as a very rough estimate):
where G is the gravitational constant, M is the mass of the Earth in kg, and P is the satellite’s orbital period in seconds.
Geosynchronous satellites have an orbital radius of 42,164 km, so our mystery satellite is almost as far out as the geosynchronous satellites. If it were further, the satellite would have been moving westward across our field of view, not eastward.
Admittedly, this is a lot of hand waving and is almost certainly wrong, but perhaps it gets us reasonably close to the right answer.
Now, let’s consider the shadow of the Earth to give us another estimate of the satellite’s distance.
At the time of observation, the Sun was located at 19h04m23s -22°36’40”. The anti-solar point, which is the center of the Earth’s shadow cone, was then located at 7h04m23s +22°36’40”. That is only 18.1° from the satellite. The Sun’s angular diameter at that time was 32.5 arcminutes. In order for the satellite to not be shadowed by the Earth, the angular diameter of the Earth as seen from the satellite must be less thanThe distance from the center of the Earth at which the Earth subtends an angle of 18.6° is given bySo, using this method, the satellite must be at an orbital radius of at least 38,905 km to be outside the Earth’s umbral shadow cone.
Now, on to something less speculative: the varying brightness of the satellite. I used Limovie to track the satellite across most of the field and got the following light curve.
At first blush, it appears the satellite is tumbling with a period of around 51.2s. But a closer inspection reveals that a larger amplitude is followed by a smaller amplitude is followed by a larger amplitude, and so on. So the tumbling period looks to me to be more like 102.4s. The mean (unfiltered) magnitude of the satellite looks to be around 11.8m, but ranging between 10.7m and 13.0m. Thus the amplitude is around 2.3 magnitudes. You will find the raw data here.
Update January 10, 2018
Alain Figer, French astronomer and satellite enthusiast, was kind enough to identify this object for me. Alain writes, “At first glance I noticed, using Calsky, that Falcon 9 rocket, 2017-025B, #42699, might be your satellite…From the MMT data (astroguard russian site) 2017-025B rotation period was measured at 89.55s on 13 OCT 2017. That figure seems to me in rather good agreement with yours at 102.4s, since the rotation period of this rocket might be quickly lengthening, a rather classical behaviour for such newly launched rockets.” Alain goes on to say, “For estimating the satellite altitude from your own observations you have to consider its highly eccentric elliptical orbit.” Thank you, Alain!
After I got home from work this evening, I began thinking, “Hmm, Guide is such an amazing program, maybe it can show me accurate satellite positions as well.” Turns out, it can! After downloading the current orbital elements for all satellites and turning on the satellite display, I was able to confirm Alain’s determination that this object is indeed Falcon 9 rocket body 2017-025B.
SpaceX launched the Inmarsat-5 F4 commercial communications satellite from historic Launch Complex 39A at NASA’s Kennedy Space Center in Florida using a Falcon 9 rocket on May 15, 2017. Here are some pictures and a video of that launch.
The Falcon 9 rocket body currently orbits the Earth once every 23h21m19s in a highly-elliptical orbit (e=0.8358) that ranges from a perigee height of 432.4 km to an apogee height of 69,783 km. During the time of observation, its range (i.e. distance from me, the observer) went from 64,388 km to 64,028 km. The semi-major axis of its orbit is 41,481 km which is 3.3% higher than my (lucky) estimate above. The shadow criterion of > 38,905 km is met as well.
Today we celebrate the 50th anniversary of the inaugural flight of Wernher von Braun’s magnum opus, the giant Saturn V moon rocket. This first flight was an unmanned mission, Apollo 4, and took place less than 10 months after the tragic launch pad fire that killed astronauts Gus Grissom, 40, Ed White, 36, and Roger Chaffee, 31.
The unmanned Apollo 4 mission was a complete success, paving the way for astronauts to go to the Moon. After another successful unmanned test flight (Apollo 6), the Saturn V rocket carried the first astronauts into space on the Apollo 8 mission in December 1968. On that mission, astronauts Frank Borman, Jim Lovell, and Bill Anders orbited the Moon for 20 hours and then returned safely to Earth.
“As of 2017, the Saturn V remains the tallest, heaviest, and most powerful (highest total impulse) rocket ever brought to operational status, and holds records for the heaviest payload launched and largest payload capacity to low Earth orbit (LEO) of 140,000 kg (310,000 lb), which included the third stage and unburned propellant needed to send the Apollo Command/Service Module and Lunar Module to the Moon. To date, the Saturn V remains the only launch vehicle to launch missions to carry humans beyond low Earth orbit.”
Reference (for quoted material above)
Wikipedia contributors, “Saturn V,” Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Saturn_V&oldid=808028027 (accessed November 9, 2017).
The last Space Shuttle flight took place in July 2011 (Atlantis, STS-135), and in going through the archives from ten years ago, I found this write-up about the International Space Station and the Space Shuttle seen together in the sky.
International Space Station & Space Shuttle – Docked
This past Sunday evening brought my family to Governor Dodge State Park north of Dodgeville for a stroll in the dark—and what we thought would be a “routine” flyover of the International Space Station. Boy, were we surprised! Even though conditions were quite hazy, the ISS made its appearance as predicted, but as it reached its culmination of 62° at 10:27 p.m. (6/17/07 CDT) we witnessed something none of us had ever seen before: a gradual brightening of the ISS to between -6 and -9 magnitude, followed by a gradual dimming back to the normal slightly negative magnitude of a favorable flyover. We had observed a “sun glint” off of the large station’s many reflective surfaces. What a treat!
Footnote #1: The ISS had a definite orangish tint to us, which may have been real in spite of the hazy conditions.
Footnote #2: No-line bifocals (progressive lenses) work well during the day, but try looking at a bright moving object at night (or stars in general) to see just how bad the optics are! For night viewing, I recommend a pair of glasses (if you need them) for distance viewing only, with glass lenses (not plastic!) and 0.5 diopter greater correction than you normally use. I have such a pair, but forgot to bring them with me that night.
International Space Station & Space Shuttle – Undocked
This past Tuesday, the Space Shuttle Atlantis (STS-117) undocked from the International Space Station, and, as luck would have it, there were two opportunities that evening to view the pair—separated by only 46 miles—cross the sky in a beautiful pas de deux. The first and best event, which culminated at 9:33 p.m. (6/19/07 CDT), was still impressive in spite of bright twilight because the spacecraft were so bright. The brighter and oranger ISS was leading Space Shuttle Atlantis by about 3° when first sighted low in the NW, which expanded to about 6° at culmination since both spacecraft were closer to Wisconsin and the axis between the two least foreshortened, shrinking again to 3° when both spacecraft disappeared into the shadow of the Earth low in the ESE. The changing orientation of the axis connecting the two spacecraft as they crossed the sky was interesting to observe.
A curious phenomenon that my wife, daughter, and I all noticed was that the positions of the two spacecraft with respect to each other seemed to “wiggle” a bit at times as they crossed the sky. What a strange optical illusion, because obviously both spacecraft were moving smoothly relative to Earth and relative to each other!
I also observed the second pass that evening, which reached a maximum altitude of only 14° in the WSW sky before the pair entered the shadow of the Earth at 11:07 p.m. CDT. Both spacecraft were about two magnitudes fainter than before, and this time Atlantis seemed brighter and oranger than the ISS!
As any double star observer knows, though, the perceived color of an object is strongly dependent upon its brightness!
Some people are molded by their admirations, others by their hostilities. – Elizabeth Bowen (1899-1973)
I have many admirations, and one of them is for a bi-weekly magazine called Science News. My first introduction to this amazing publication was in 1973, when a friend of my recently-divorced mother, Frank Gillotti, started giving me his copies after he was finished reading them. I was a sophomore at Hoover High School in Des Moines then, and by my senior year I was a subscriber for life.
Science News has been around a long time. It started way back in 1922 as Science News-Letter, and remained that until 1966, when it became Science News. Today, Science News has an international circulation of about 94,000—alarmingly, down quite a bit (like most magazines) from its peak circulation of nearly 250,000 in the late 1980s. Unlike most magazines these days, Science News is not saturated with advertising, but is instead chock-full of well-written, accurate, and timely news and feature articles about all areas of science, technology, and mathematics. Yes, astronomy and space science are covered thoroughly! And, with each bi-weekly1 issue numbering 32 pages (though, occasionally 40+), it is easy to find the time to read or at least skim it cover-to-cover every two weeks.
In my early years reading Science News, one writer I particularly admired was senior editor / physics editor Dietrick E. Thomsen, whom I was so fortunate to meet at the AAS Meeting in Ames, Iowa in June 1986. Sadly, he passed away in 1988. One thing I remember about him besides his always-excellent articles was his passion for passenger trains, and his growing distaste for air travel at the time (and it has only gotten worse). At that time, I had never ridden on a passenger train, but nowadays I ride Amtrak regularly, and love it!
Another fantastic writer in those days at Science News was space science editor Jonathan Eberhart (1942-2003) whose brilliant and unconventional career was sidelined by multiple sclerosis by 1991. The AAS Division for Planetary Sciences (DPS) has awarded the Jonathan Eberhart Planetary Sciences Journalism Award annually since 2009. J. Kelly Beatty (Sky & Telescope) was the first recipient (in 2009), andEmily Lakdawalla (The Planetary Society) won the 2011 award.
Science News maintains an excellent web site. One feature I really like is they provide a complete list of sources and references for their magazine articles.
And, Society for Science & the Public (SSP), the nonprofit corporation that produces Science News, also produces an excellent website for readers ages 9-14, Science News for Students.
Check out these wonderful resources regularly, and while you’re at it, don’t forget to subscribe!
1Science News published weekly through April 12, 2008. Science News began publishing bi-weekly on May 10, 2008.
Wednesday evening, September 13, 2017, at 9:59 p.m. CDT, Saturn reaches eastern quadrature as Saturn, Earth, and Sun form a right triangle. Eastern quadrature is so named as Saturn is 90° east of the Sun. This is the time when Saturn presents to us its most gibbous phase. Even so, Saturn will be 99.7% illuminated due to its great distance from us.
Saturn will only be 12° above our horizon in SW Wisconsin at the exact moment of eastern quadrature Wednesday evening. Earlier that evening, Saturn crosses the celestial meridian at 6:51 p.m.—22 minutes before sunset. If it weren’t for daylight, that would be the best time to observe Saturn: when it is highest in the sky and we are seeing it through the least amount of atmosphere. If you have a telescope equipped with a polarizing filter, you can significantly darken the blue sky background around Saturn since the planet will be exactly 90° away from the Sun, where the scattered sunlight is most highly polarized. Rotate the polarizer until the sky is darkest around Saturn.
Speaking of Saturn, the Cassini mission will come to a bittersweet end on Friday, September 15 around 5:31 a.m. CDT when the storied spacecraft, which has been orbiting Saturn since June 30, 2004, will have plunged deep enough into Saturn’s atmosphere that it is no longer able to point its high gain antenna towards Earth. Soon after that, Cassini will burn up in Saturn’s massive atmosphere. We on Earth will not receive Cassini’s last radio transmission until 1h23m later—at around 6:54 a.m. CDT.
Emily Lakdawalla, who is arguably the best planetary science journalist in the world these days, includes the visual timeline of Cassini’s demise shown below and in her recent blog entry, “What to expect during Cassini’s final hours”.
Also, on Wednesday evening, don’t miss NOVA: Death Dive to Saturn, which will air on Wisconsin Public Television’s flagship channel at 8:00 p.m.
It may be a while before we visit ringed Saturn and its retinue of moons again. But further exploration of Titan and Enceladus is certain to feature prominently in humankind’s next mission to Saturn. Hopefully, that will be soon.
Edmund Weiss (1837-1917) and many astronomers since have called asteroids “vermin of the sky”, but since October 4, 1957 another “species” of sky vermin made their debut: artificial satellites. In the process of video recording stars for possible asteroid occultations, I frequently see satellites passing through my ~¼° field of view.
I’ve put together a video montage of satellites I’ve recorded between December 14, 2016 and August 5, 2017. The component events are presented chronologically as follows:
7-25-2017 (2 satellites)
In all cases, the asteroids were too faint to be recorded. And, in all cases, the target star was not occulted by the asteroid (a miss). In the final event, the satellite passed right over the target star (9:40:11.679 UT) during the period of time the event would be most likely to occur (9:40:10 ± 3 s)! Fortunately, the seeing disc of the target star was never completely obliterated by the passing satellite, so I was able to determine unequivocally that the asteroid missed passing in front of the star from my location on Spaceship Earth.
Here’s a graph of the brightness of UCAC4 548-7392 during the last video clip. You can definitely see the close appulse of the satellite with the star!
In general, the slower the satellite is moving across the field, the higher is its orbit around the Earth. One must also consider how much of the satellite’s orbital motion is along your line of sight to the satellite. In the following montage of two video clips, the first satellite is very slow moving and thus most likely in a very high orbit. The second video clip shows a satellite that is quite faint. Again, the asteroids are too faint to be recorded and no asteroid occultation event occurred.
190471 (2000 DG27)
321656 (2010 BM90)
Hughes, D. W. & Marsden, B. G. 2007, J. Astron. Hist. Heritage, 10, 21
Every once in a while a really great documentary comes along. In the Shadow of the Moon is one of them. This 2007 British film, which like most documentaries (unfortunately), had a very limited theater engagement, is now widely available for rental or purchase.
The historical importance of this documentary cannot be overstated. There is nothing, and I mean nothing, like hearing about the first (and still only) human missions to the Moon firsthand from the astronauts who journeyed there. And, sadly, these pioneering astronauts are not going to be with us much longer. Some have already left us. In the eleven years since this documentary was released, Edgar Mitchell, the last surviving member of the Apollo 14 crew, passed away in 2016, Gene Cernan, the last man to walk on the Moon, passed away in 2017, and John Young, the longest-serving astronaut in NASA history, left us in 2018. The seven surviving Apollo astronauts who shared their stories with us in this film are all octogenarians: Buzz Aldrin is 87, Michael Collins is 87, Alan Bean is 85, Jim Lovell is 89, David Scott is 85, Charles Duke is 82, and Harrison Schmitt is 82.
John Glenn, the oldest of the Project Mercury astronauts and the first American to orbit the Earth, was the last to die, in 2016, at the age of 95.
Gus Grissom (1967) – Apollo 1 launch pad fire
Deke Slayton (1993) – brain tumor
Alan Shepard (1998) – leukemia
Gordon Cooper (2004) – Parkinson’s disease; heart failure
Wally Schirra (2007) – abdominal cancer; heart attack
Scott Carpenter (2013) – complications following a stroke
John Glenn (2016) – complications after heart valve replacement, stroke
Walter Cronkite (1916-2009) and Wally Schirra (1923-2007) covered the Apollo moon missions on CBS—far better than anyone else—and I can still remember the events as if they happened only recently.
Want to know who holds the title for longest duration human spaceflight (so far)? Valeri Polyakov (1942-) entered space aboard Soyuz TM-18 on January 8, 1994 and stayed aboard the Mir space station until returning to Earth aboard Soyuz TM-20 on March 22, 1995. That’s nearly 438 days (1.2 years) in space! Moreover, Polyakov, who is a medical doctor, spent over 240 days in space during his first visit to Mir in 1988-1989, giving a total spaceflight time of nearly 1.9 years.
While Polyakov still holds the record for the single longest duration spaceflight, Gennady Padalka (1958-) has spent more time in space than anyone else: 878.5 days (2.4 years)!