PREFACE

                                                                   Exhibit 10.21

           SECOND AMENDMENT TO SERIES A SUBORDINATED CONVERTIBLE NOTE

         THIS SECOND AMENDMENT TO SERIES A SUBORDINATED CONVERTIBLE NOTE
("Amendment") is made this 25th day of March 2003, by and between SpaceDev,
Inc., a Colorado corporation (the "Company") and Xxxxx X. Xxxxxxx (the
"Holder").

                                     PREFACE

         WHEREAS, Holder invested in those certain Series A Subordinated
Convertible Notes of the Company pursuant to a Note Purchase Agreement and
Series A Subordinated Convertible Note (the "Note") dated October 29, 2002 in
the principal amount of Fifty Thousand Dollars ($50,000.00); and

         WHEREAS, Holder and the Company desire the extend the repayment period
of the Note by an additional six (6) months as provided in this Amendment;

         NOW THEREFORE, the Note is amended as provided in this Amendment.

                                    ARTICLE I

         Section 1.1 of the Note is stricken in its entirety and amended to read
as follows:

         "1.1 PAYMENT. Subject to the provisions of Section 2 hereof relating to
the conversion of this Note, principal and accrued interest hereof shall be
payable on the twelve-month anniversary hereof (the "MATURITY DATE").

         Payments hereunder shall be made by the Company to the Holder, at the
address as provided to the Company by the Holder in writing, in lawful money of
the United States of America. Interest shall accrue with respect to the unpaid
principal amount of the loan from the date of this Note until such principal is
paid or converted as provided in Section 2 hereof at a rate of 2.03% per annum
(computed on the basis of a 365-day year)."

                                   ARTICLE II

         This Amendment to the Note may be executed in any number of
counterparts, each of which, when taken together, shall be deemed the fully
executed agreement between the parties.

         IN WITNESS WHEREOF, the parties have executed this Amendment effective
March 25, 2003.

HOLDER                               THE COMPANY

/s/ Xxxxx X. Xxxxxxx                 By: /s/ Xxxxx X. Xxxxxx
-----------------------------        -------------------------------------------
Xxxxx X. Xxxxxxx                     Xxxxx X. Xxxxxx, Chief Executive Officer


                                     By:  /s/ Xxxxxxx X. Xxxxxxx
                                         ---------------------------------------
                                     Xxxxxxx X. Xxxxxxx, Chief Financial Officer