Vehicle airbag system

1. A vehicle, comprising:

a first seat;

a second seat;

a bulkhead elongated along an axis;

a base supported by the bulkhead and inflatable from a stowed position away from the bulkhead to a deployed position; and

an airbag supported by the base and inflatable away from the bulkhead and the base to an inflated position, the airbag in the inflated position having a main portion and extensions extending away from the main portion along a vehicle-longitudinal axis, the extensions including a first extension outboard of the first seat, a second extension outboard of the second seat, and a third extension between the first seat and the second seat, the extensions being spaced from each other along the axis.

2. The vehicle of claim 1 , wherein the base includes side walls that define an inflation chamber and are a thermoplastic elastomer, and wherein the airbag includes woven fabric that defines a second inflation chamber.

3. The vehicle of claim 1 , wherein the main portion of the airbag in the inflated position defines a main chamber and the extensions of the airbag in the inflated position define extension chambers, and wherein the airbag in the inflated position includes internal panels separating the main chamber from the extension chambers.

4. The vehicle of claim 3 , wherein the internal panels include one-way valves that permit fluid flow into the extension chambers and inhibit fluid flow out of the extension chambers.

5. The vehicle of claim 1 , wherein the airbag includes an impact panel between the first extension and the second extension, and wherein the impact panel is concave away from the first seat.

6. The vehicle of claim 5 , wherein the airbag includes an internal tether fixed to the impact panel between the first extension and the second extension.

7. The vehicle of claim 1 , wherein the extensions include distal ends, and wherein the airbag includes internal tethers fixed to the distal ends of the extensions.

8. The vehicle of claim 7 , wherein the internal tethers extend into the main chamber.

9. The vehicle of claim 1 , further comprising a second base supported by the bulkhead and inflatable from a second stowed position away from the bulkhead to a second deployed position, the airbag supported by the second base.

10. The vehicle of claim 9 , wherein the base is spaced from the second base along the axis.

11. The vehicle of claim 10 , further comprising an external tether fixed to the airbag and the bulkhead.

12. The vehicle of claim 1 , further comprising an inflator in fluid communication with the airbag and the base.

13. The vehicle of claim 1 , further comprising a seat facing the bulkhead, the seat having a seatback, the seatback being reclinable, the airbag in the inflated position being in front of the seat.

14. The vehicle of claim 13 , further comprising a computer having a processor and a memory storing instructions executable by the processor to:

in response to both detecting that a recline angle of the seatback is greater than a threshold and based on information from an impact sensor, command the base to the deployed position and command the airbag to the inflated position, and

in response to both detecting that the recline angle of the seatback is not greater than the threshold and based on information from the impact sensor, command the airbag to the inflated position and refrain from commanding the base to the deployed position.

15. A vehicle, comprising:

a bulkhead;

a first base supported by the bulkhead and inflatable from a stowed position away from the bulkhead to a deployed position;

a second base supported by the bulkhead and inflatable from a second stowed position away from the bulkhead to a second deployed position; and

an airbag supported by the first base and the second base, the airbag inflatable away from the bulkhead and the base to an inflated position.

16. The vehicle of claim 15 , wherein the first base defines a first base chamber and the second base defines a second base chamber fluidly separated from the first base chamber.

17. The vehicle of claim 15 , further comprising an inflator in fluid communication with the first base, the second base, and the airbag.

18. The vehicle of claim 15 , wherein the first base and the second base each include thermoplastic and the airbag includes woven fabric.

19. The vehicle of claim 15 , further comprising a first tether fixed to the airbag and fixed to the bulkhead at the first base, and further comprising a second tether fixed to the airbag and fixed to the bulkhead at the second base.