The ZeroG website gives a broad overview of what you get for your $4K, but I thought I'd set down my impressions while they are fresh in my mind.
The whole process takes about 5-6 hours. You arrive at the meeting place (in our case, an airport hotel) and check in, and you're given your flight-suit, a carry-bag, and a plastic nametag, which, according to long-standing astronaut tradition, is worn upside down if you haven't flown before. You get introduced to your coach (ours was a former passenger who finagled a job for herself; James' reaction to this news was to inquire if summer jobs were available!), who is overly enthusiastic about what you're about to experience, etc., etc., etc. It is at this point that you will start thinking they're laying it on a bit thick; in a few hours, you will change your mind.
Each coach handles a group of about 10 people; you get color-coded badges and socks that identify what group (blue, gold or grey) that you're in.
In our case, we also had a meeting with the TSA security team for final approval of our experiments. They'd been completely briefed on what we wanted to do, so there were no real surprises.
Then you sit down for a light low-protein meal (it helps settle the stomach, and carbs soak up any acid overproduction) and watch a 35-minute video that goes through the details of the flight, safety precautions, and so on. It's at this point that you take your motion-sickness meds if you've decided to use them; we did, though now that we've done it, in retrospect we probably didn't need to. On our flight, one person got a little queasy, but only after the actual parabolic segments!
When that's all done, you go through TSA screening, get on a party bus (ours had a stripper pole!), and go out to the plane.
Once onboard (through the rear stairs), you get the usual safety briefing. Since the flight operates under the normal airline rules, it has to have a trained flight attendant aboard in addition to the coaches, flight director, and pilots (at least, we think there were some pilots aboard, we never saw them for some reason). While there was a cute comedy moment in the briefing, they need to add something to it along the lines of "in case of sudden loss of cabin gravity, a silly grin will appear on your face."
The seating area is at the rear of the plane, and the floating area is divided into 3 zones, one for each group.
The FAA clears a block of airspace for exclusive use by G-Force One (I still think it should be called G-Force Zero), and it takes about 30 minutes for the plane to get there. Then everyone moves to the floating area for a final briefing.
The floating area is heavily padded, but if you come out of a zero G segment upside down and near the roof, you might bang yourself up, which is why at the end of each segment there's a warning so you can get oriented. The transitions to and from freefall take several seconds so you have plenty of time to set yourself up; you'd really have to work at it to get hurt doing this.
There are no windows in the cabin except for the emergency exit windows; this apparently helps reduce the chances of motion sickness by removing external cues about your orientation. In addition to a photographer who literally floats around taking pictures of everyone, there are 6 HD cameras installed in the floating areas. Several weeks after the flight, you will get an edited video plus all the raw footage.
Each complete parabolic cycle is about 55% 1.8G and 45% 0G (the books have to balance, so to speak). During the 1.8G segments you are advised to lie on your back and stare at a point on the ceiling (another anti-motion-sickness trick). I tried other positions later in the flight with no ill-effects.
Each flight contains 15 parabolic segments, divided into 3 groups of 5. The freefall periods last around 25 seconds; they feel like they are much longer while you are doing them, and much shorter after it's all over. Between each group there are 3-5 minutes of normal flying while the airplane does a 180 to keep within the assigned airspace. This turned out to be very handy, as during the last break, James and I went into the seated area and got set up for the Diet Coke & Mentos experiment, which we did using the light from the emergency exit porthole. We did the experiment for two parabolas, then on the next one, we unbelted ourselves and swam back up the aisle and into the main cabin area, a very cool maneuver.
To ease you into things, the first parabola is at 1/3G (Martian gravity) and the next two are at 1/6G (Lunar gravity). You can do all sorts of goofy stuff like one-handed pushups, pushups to standing position, and the lunar "bunny hop" gait that the Apollo astronauts used to get around.
Then you go to full freefall. And I cannot emphasize this enough: in freefall, you do not feel like you are falling! For me this was by far the most surprising aspect of the experience. I expected it to be like going over a hill on a roller-coaster, or like one of the "drop" rides (which I hate). It was nothing like that at all!
I can be an eloquent bastard from time to time, but I am having real trouble describing what it feels like, because there simply are no words in any language to describe it. But anyway, here goes: it is not so much a sensation as it is the lack of a sensation, one you've felt all your life, one that is so much a part of your daily experience that you do not notice it. The closest you could come to it without actually going into freefall would be scuba diving, but there's a crucial difference. Even when you're neutrally buoyant underwater, if you focus really hard, you can still feel gravity tugging at your insides, pushing your organs against your muscles. In freefall, even that is gone. Once you experience it, you will know the answer to the famous Zen koan, "What is the sound of one hand clapping?" And you will literally be "enlightened".
During the first 7 freefall segments, there's various activities that typically get done; eating M&M's, playing with water spheres, etc. The last 5 segments are free-format playtime. If I have one regret about the flight, it was that I didn't spend one of those segments just floating in midair, eyes closed, doing nothing. I'll know better next time.
And that brings up a word of caution: you need to understand that this flight doesn't cost $4,000. It costs at least $8,000 -- because once is not enough. The first thing Natsumi said to me when we were sitting down, flying back to the airport, was "We have to do this again!" Yes! My kind of woman!
After the parabolic flying is done, there's the 30 minute flight back to the airport. As you descend down the stairs, your badge is ceremonially turned rightside-up by the flight director. After some photos, it's back to the hotel for a light lunch and the distribution of flight certificates. You get a nice totebag, and you get to keep your badge and flightsuit.
Which, of course, you'll need when you go on your next flight.