Independence Day 2006 looms fairly large among the memories of United States astronaut Stephanie Wilson.
On July 4 that year, at 39, an age at which others might have been contemplating somewhat different milestones in life, Wilson was aboard space shuttle Discovery, being thrust into space for the first time (and at a speed of 28,000kmh, or almost 8km per second).
Yet ask Wilson whether she felt excited, anxious or otherwise on that day, and the veteran of three space flights - she has logged more than 42 days in space - offers a vision of professional calm.
"For shuttle training we spend several hundred hours in simulators. In some ways the surprise is taken out of it. It becomes ... routine."
"I believe we had about 3500 astronaut applicants that year. Thirty-five were selected from the United States and nine from elsewhere, so we had a class of 44 in total. Of those selected, all but three have gone into space."
Another three members of that class never made it back from orbit.
They were among the seven crew members killed when Columbia disintegrated over Texas and Louisiana during re-entry into Earth's atmosphere on February 1, 2003.
"I had trained with that crew so I could be familiar with their operations and speak with them during their flight," recalls Wilson, who was working in "mission control" as a key communicator with on-orbit crews at the time.
"We were all close. It was a great tragedy and was felt deeply throughout Nasa."
The result of damage sustained during launch when a piece of foam insulation the size of a briefcase broke off from an external fuel tank and compromised the vessel's thermal protection system (which shields it from the intense heat generated during re-entry), the Columbia disaster did more than evoke memories of Challenger, which broke up just 73 seconds after its launch in 1986, killing all seven crew members.
In fact, it shut down Nasa's shuttle programme for two and a-half years.
And when it did resume with the launch on July 26, 2005, of Discovery, that mission was also not without incident as the problem that resulted in the destruction of Colombia recurred. As a result, Nasa decided to postpone future shuttle flights pending additional modifications to flight hardware.
Enter Wilson.
Her debut space flight was next on the Nasa schedule. The 12-day mission included "procedures to increase the safety of space shuttles", with Wilson's specific responsibilities involving robotic arm operations for vehicle inspection, multipurpose logistics module installation and the transfer of supplies and equipment to the International Space Station.
"It [the Columbia disaster] made us resolved to make sure we had a thorough investigation, to ensure subsequent flights went ahead. We wanted to honour the crew's dedication by continuing the work they had started.
"Also by spending that much time in training, spending so much time in the vehicles, we have great confidence in the people who have built those systems and those who have done all the checks and balances to ensure safety. By the time we arrive at launch day we are sure everything that can be checked has been checked."
Yet the mission that looms most vividly for Wilson was not her first, but rather her second.
Again taking off in Discovery, on October 23, 2007, she spent 15 days in space, serving as flight engineer, assisting the commander and pilot, as the shuttle delivered a module named "Harmony" to the International Space Station. This element opened up the capability for future international laboratories to be added to the station; in Wilson's words: "It was regarded as a gateway to future science".
"We ran into some trouble, so we had to do a contingency spacewalk. That involved the flight control team, the training team, the space walking and robotics teams ... they all had to come together to come up with a plan to repair the solar array. We could only use the items we had on board."
It has been two years since Wilson last saw Earth from afar (she was part of a Discovery resupply mission to the International Space Station in April 2010). And though such a first-hand perspective is limited to a relatively small group, she performs a deft manoeuvre when asked if astronauts are regarded as the cream of the crop.
"For those astronauts who are civilians - like myself - we are part of the US Government's civil service workforce. The way we advance in our career is the same as other federal organisations," she explains, pausing oh so briefly before adding: "But one great perk is we have the opportunity to go into space."
It's a spectacular feeling being in space, she says. It is also very humbling.
"The colours are very vivid. I could distinguish features such as canyons and mountains, deserts, lush lands, the deep blue of the oceans. It is also very peaceful. Borders are not visible, nor is any strife that could be occurring.
"It reminds me that we are one small planet in a large universe. Seeing the transit of Venus [last week] puts that into perspective. It also reminds us of how fragile Earth is and how we must do all we can to protect it for future generations."
Wilson hopes to add to her three space flights with a six-month stay in the International Space Station, though she has yet to be assigned to a specific mission.
If - or when, given her proven professional record so far - she goes, Wilson knows the assignment will be tougher than any of her shuttle experiences.
"Certainly, for a two-week flight on the shuttle, the return to Earth is actually pretty benign. For the first day or so it feels as if your body is very heavy. There is also a sensation of falling or spinning, a little bit like vertigo, and that goes away after about a day. It's like having been on a boat for an extended time.
"However, if you're on the International Space Station for six months, well, that's a much bigger deal.
"The return is much harder on the body; the recovery is more extensive and more regimented. We have personal trainers at Nasa and they have a very specific regimen for recovering strength and reflexive responses, such as running or catching a ball."
In comparison to a space shuttle flight, which requires about a year's specific training, there is a two and a-half year regime that accompanies a space station internment, including familiarisation with Russian, Japanese and European laboratories as well as those of her own nation's scientists; she would also face Russian language lessons.
It's a far cry from 1958, the year United States President Dwight Eisenhower established Nasa following the Soviet Union's Sputnik success. Launched on October 4, 1957, the first man-made object to be placed into Earth orbit signalled the start of a space race that culminated in the United States' Apollo 11 mission to the moon in July, 1969.
"We have cosmonauts here at Johnson Space Centre; we regularly see them training on systems," Wilson says of the current climate of international co-operation.
"Perhaps for our veteran astronauts - those who flew Apollo missions or in the early days of shuttles - it would come as more of a surprise than for those of us who have arrived more recently.
"When I arrived at Nasa, a lot of the plans for the International Space Station were well under way," she says of the project, the first module of which was launched by a Russian rocket in 1998.
"The climate I'm used to is collaborative. It seems very natural to me."
Nasa plans to go deeper
The implications of news reports last week of space shuttle Enterprise being towed along the Hudson River, New York, where it faces a future as a floating museum, were not lost on United States astronaut Stephanie Wilson.
After all, Wilson was orbiting Earth in a similar machine, Discovery, just two years ago.
Like the other shuttles, Discovery has been decommissioned. In April it was attached to a modified 747 jumbo jet for transport to the Smithsonian's National Air and Space Museum in Virginia. Of the remaining shuttles, Endeavour will move to a Los Angeles facility in mid-September, and early next year Atlantis will go on permanent display at Kennedy Space Centre, Florida.
"The shuttle was designed with 1960s and '70s technology so from that perspective ... that is one of the reasons why we thought it best to retire them."
What then does the future hold for Nasa?
"At this point, the direction Nasa has been given has been to foster travel to low-Earth orbit, say to the International Space Station, by commercial entities, including other aerospace companies.
"Nasa would then focus on travel outside of low-Earth orbit - that is, to Mars or back to the moon or to an asteroid. The destination has yet to be determined. The current presidential administration would like Nasa to focus on deep space.
"Nasa's Marshall Commercial Spaceflight Centre in Huntsville, Alabama, is working heavily on the launch vehicle capabilities that would take us beyond low-Earth orbit."
Countdown to takeoff
"As a teenager, I wanted to be an astronaut. I had a school assignment that required me to interview someone from a career field I was interested in. At the time I wanted to be an astronomer so I talked to a local astronomer in a small town near Pittsfield.
"That was the beginning of my interest in space. I was also interested in design and eventually decided to study engineering but maintained an interest in space."
The ensuing years are a blueprint of personal application.
After graduating from Harvard University in 1988 with a bachelor of science degree (engineering science), Wilson spent two years at the former Martin Marietta Astronautics Group in Denver, Colorado, then returned to tertiary study, gaining a master of science degree in aerospace engineering from the University of Texas in 1992 before joining Nasa's Jet Propulsion Laboratory in Pasadena, California, that year.
After being selected for Nasa's Astronaut Office in 1996, she completed two years of training and evaluation. Qualifying for flight assignment as a mission specialist, she was initially assigned technical duties in the astronaut office space station operations branch to work with space station payload displays and procedures.
She then worked in Mission Control as a prime communicator with in-orbit crews, later being assigned technical duties in the shuttle operations branch involving the space shuttle main engines, external tank and solid rocket boosters.
Wilson is now involved in support operations for the International Space Station.
"We deal with systems, payloads, tailoring cargo vehicles that dock with the space station. We also often preview items before crews are trained in operating that particular item of software or hardware."
The festival
In keeping with the New Zealand International Science Festival theme of "What makes us tick?", Stephanie Wilson will be involved in workshops for children, a family fun quiz night, presentations in Wall Street mall on July 4 (United States Independence Day) and an evening presentation open to the public. The New Zealand International Science Festival will be held in Dunedin from June 30 to July 8.
