The strange craft which fleeted across South Africa's night skies on Sunday the 18th of October 2009 causing UFO reports to flood observatories and Radio 702. Most people in South Africa thought they had seen a UFO but this object turned out to be a Centaur rocket carrying out tests when they passed over South Africa. From Mitchell Krog's Astrophotography Portfolio. (Copyright Mitchell Krog - All Rights Reserved)

Information from http://www.planetarium.co.za/ thanks to Claire from the Planetarium for doing so much research into this event.

Hundreds of South Africans saw a star-like point moving across the sky while emitting “haloes” or “bubbles” of light just before 9pm on Sunday evening October 18th. This strange sight turns out to have been a Centaur rocket carrying out tests as it passed over South Africa nearly three hours after launch. The mission (AV-017) is a project of United Launch Alliance – see ulalaunch.com for a nice video of the launch and a 23-page “mission overview”. The purpose was to launch a US Defence Force weather satellite (DMSP F18) into orbit.

Event timeline (all times are South African time)

6:12pm – Atlas V rocket launches from Vandenberg Airforce Base

6:16pm – booster rocket shuts down and is jettisoned over the Pacific

– Centaur main engine starts

– payload fairing jettisoned

6:27pm – Centaur main engine shuts down

6:30pm – satellite released

– Collision and Contamination Avoidance Maneuver

6:46pm – testing begins

8:57pm – testing ends

9:10pm – Centaur main engine fires for 4min to send the rocket away from Earth (into an Earth-escape trajectory)

9:17pm – “blowdown” of the fuel tanks

9:56pm – burn off of residual hydrazine

What caused the bubbles?

Possibly venting of fuel during the tests, or firing of “reaction control” motors used to change the orientation or spin of the vehicle.

Tests carried out on the Centaur

Since the DMSP satellite was relatively light, the Centaur rocket had fuel left over after completing its mission of putting the satellite into orbit.  The collision and contamination avoidance manoeuvre gets the rocket a safe distance from the satellite.

After this, the Centaur is in free-fall – a (almost) zero-gravity state that can be created on Earth for a short time by dropping something from e.g. a tall tower, or in a plane for a few minutes (e.g. NASA’s “Vomit Comet“).  The test phase of the Centaur lasted about two hours.

The tests carried out during this time were described by ULA as:

“zero-g, long-coast propellant management . . . we do zero-g settling by very reduced motion of the settling thrusters . . . [and then] settle the propellants against the wall of the tank by spinning the stage with no settling thrusters . . . [and] some venting during zero-g.”

Before re-starting the engine, the engineers also planned “a pulsed chilldown demo . . . then some experiments related to the depletion of [the engine]“

One interesting use for these tests is to see how feasible orbiting “filling stations” are.  These would be useful for future manned spacecraft missions to the Moon or Mars, that would have to carry large (heavy) amounts of equipment into space.  Some of the experiments that would be useful for the design of these orbiting “propellant depots” include spinning the spacecraft to settle the fuel against the sides of the container, and firing small rockets or venting small amounts of fuel to push the fuel against one end of the container.  A large fuel tanker in zero-gravity has problems that include leakage of the hydrogen fuel (hydrogen molecules are very small and eventually leak through the walls of containers), and keeping the fuel cool.

United Launch Alliance has a great collection of (fairly technical) publications related to the future development of space exploration – see their publications page, especially this one which mentions using the DMSP-18 mission for zero-g propellant tests.

"The mothership is watching us". What many would love to believe was a UFO turns out to be something actually from this world. A centaur rocket is captured dumping excess propellant into the atmosphere as part of a testing phase of this rocket launch. From Mitchell Krog's Astrophotography Portfolio. (Copyright Mitchell Krog - All Rights Reserved)

If you would like to order prints

of Mitchell Krog’s images above please visit www.livingcanvas.co.za and send an enquiry form through and someone will get back to you with pricing and shipping info. Details on the front page of the web site.

More articles at: http://selenianboondocks.com/2009/10/av-017-bubbling-ufos-and-centrifugal-settling/

A massive lightning strike dwarfs Pretoria, the capital city of South Africa. From Mitchell Krog's Lightning Photography Portfolios. (Copyright Mitchell Krog - All Rights Reserved)

This image will soon be available in print, watch this site for more details to be announced soon.

The Voortrekker Monument with the Magaliesburg Mountains in the Distance Photographed from Fort Schanskop in Pretoria. From Mitchell Krog's Urban Landscape Photography Portfolio. (Copyright Mitchell Krog - All Rights Reserved)

South African landscape photographer Mitchell Krog often travels to various locations around South Africa, no matter where he ends up he always seems to find a landscape photography opportunity, be it pristine landscapes or cities full of human elements. It’s all about conditioning, says Mitchell, too many photographers have conditioned their minds to thinking a landscape photograph must be “pure” and “pristine” when quite simply life and our planet is just not that way. We are after all humans and as photographers we should not only seek out untouched landscapes but also from time to time include evidence of our impact on the planet in photographs, including human elements can often add great impact to images.

The Iconic Telkom Tower and The University of South Africa UNISA Buildings at Night Photographed from Fort Schanskop Near the Voortrekker Monument Just Outside Pretoria. From Mitchell Krog's Urban Night Photography Portfolio. (Copyright Mitchell Krog - All Rights Reserved)

Cities are full of exciting things to photograph. Virtually every city in South Africa has a history going back 100 years or more, there are monuments, museums and lots of modern architecture just begging to be photographed. Of course crime in South Africa is always of concern to a photographer but there is a multitude of safe locations around city centre’s and for those safety conscious individuals, shooting in groups is often advisable. Botanical gardens offer a safe haven for photographers and most major cities in South Africa have one with very reasonable access fees, some even free.

The International Space Station Fleeted Across the South African Night Skies on The 30th of August 2009 at 6:51pm. From Mitchell Krog's AstroPhotography Portfolio. (Copyright Mitchell Krog - All Rights Reserved)

More photos here.
ISS Discussion on SARL Web site.